Finding, Qualifying, and Using Prior Art: A Practical Guide

Two weeks after the complaint is served, an engineer at the defendant sends a one-line email: "I'm pretty sure the old Vortiq manual described exactly this, and I think it was on their website." Most invalidity defenses begin with a sentence like that, and the sentence is worth nothing until someone finds the manual, proves when and how the public could get it, shows that it describes every element of the claim, and gets it admitted. This guide is about turning "I'm pretty sure" into evidence, and about how a patent owner takes that evidence apart.

The short answer

Prior art work has six stages, and each has its own failure mode:

1. Fix the target. Identify the asserted or pending claims, construe the key terms, and determine each claim's effective filing date and whether the AIA or pre-AIA version of 35 U.S.C. § 102 governs.
2. Search three universes. Patent documents, non-patent literature, and products, including the patent owner's own launches, demonstrations, and sales.
3. Qualify each candidate. Category, date, public accessibility (or public or commercial character, for uses and sales), content, enablement, and the § 102(b) exceptions.
4. Prove it. Authenticate documents, corroborate testimony, and lock down the provenance of physical products.
5. Chart it. Element by element for anticipation; reference by reference, with reasons to combine, for obviousness under 35 U.S.C. § 103.
6. Deploy it in the right forum, on time. In prosecution through information disclosure statements and declarations; in litigation through contentions, expert reports, and the notice required by 35 U.S.C. § 282; at the Patent Trial and Appeal Board only if the art is a patent or printed publication.

The doctrine behind each stage is explained in Prior Art Under the America Invents Act: Section 102, the On-Sale Bar, Public Use, and the One-Year Grace Period. This guide is the procedure.

The framework in one table

The Board's limitation to patents and printed publications comes from 35 U.S.C. § 311(b), and reexamination is limited the same way by 35 U.S.C. § 302. Post-grant review, available only for nine months after grant of an AIA patent, takes any ground under 35 U.S.C. § 321(b).

Step 1: Fix the target: claims, effective filing dates, and the governing statute

Everything downstream depends on two things you settle first: what the claims require and the date against which art is measured.

Read the claims and pick the working constructions. List each independent and asserted dependent claim and break it into lettered elements. Flag terms whose meaning will decide anticipation (for example, "automatically," "continuous," "integral"). Use the ordinary meaning in light of the specification and prosecution history under Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005) (en banc), and run searches under both the broad and the narrow reading of any disputed term. Remember that a construction broad enough to read on the accused product may also read on the art, a squeeze every experienced defendant uses. The mechanics are in Claim Construction and Markman Hearings: How Courts Decide What a Patent Actually Covers.

Map the priority chain and date each claim. Pull the file history and every application in the chain: provisionals, parents, foreign priority applications under 35 U.S.C. § 119, and domestic benefit claims under 35 U.S.C. § 120. For each claim, ask whether each earlier application provides written description support under 35 U.S.C. § 112(a). A claim that loses its earliest date can fall to the patent owner's own intervening activity, which is exactly what happened in New Railhead Manufacturing, L.L.C. v. Vermeer Manufacturing Co., 298 F.3d 1290 (Fed. Cir. 2002).

Pick the statute. Claims with an effective filing date on or after March 16, 2013 are governed by the AIA (an application that contains, or ever contained, even one such claim is an AIA application). Older claims are governed by pre-AIA § 102, which measures most art against the date of invention and allows the patent owner to antedate references. Record the answer at the top of the file, because it changes what you search for: foreign public uses and sales count against AIA patents but not pre-AIA patents, and secret prior invention by a third party counts only against pre-AIA patents.

Compute the critical dates. For AIA claims there are two: the effective filing date (third-party disclosures before it are prior art unless an exception applies) and the date one year earlier (the patent owner's own disclosures before it are prior art without exception). For pre-AIA claims, the critical date for the statutory bars is one year before the earliest U.S. filing date to which the claim is entitled (a U.S. provisional or parent application counts; a foreign priority date does not), and the invention date governs § 102(a), (e), and (g).

Decision point. If any claim looks vulnerable on priority, start the patent owner history investigation (Step 5) first. It is usually the cheapest invalidity theory and often the strongest.

Step 2: Build the search plan

A search plan is a short written document that tells searchers what they are looking for, where, and when to stop. Writing it forces the team to agree on what "relevant" means and gives you a record to defend later, which matters because IPR estoppel turns on what "a skilled searcher conducting a diligent search reasonably could have been expected to discover," Ironburg Inventions Ltd. v. Valve Corp., 64 F.4th 1274 (Fed. Cir. 2023).

1. Element map. For each claim element, list synonyms, functional equivalents, and the older vocabulary the field used before the patent's terminology became common.
2. Classification. Collect the Cooperative Patent Classification (CPC) codes on the patent, on the references it cites, and on its foreign family members. Classification searching finds art that keyword searching misses, especially in older and foreign documents.
3. Time window. Search up to the effective filing date (and up to the earlier invention date for pre-AIA claims), and do not stop at the critical date: later documents can show what was known, help with obviousness motivation, or reveal earlier products.
4. People and companies. List the patent owner, its competitors, the inventors' former employers, universities with labs in the field, standards bodies, and key suppliers.
5. Languages and jurisdictions. Decide whether to search Japanese, Chinese, Korean, and German documents. Machine translations are adequate for screening; certified translations are needed for anything you will rely on.
6. Budget and stopping rules. Decide how many hours each universe gets and what result ends the search (for example, two references that each anticipate the independent claims under the narrow construction).

Assign the work deliberately. In-house engineers know the history but are poor witnesses about their own searching. Professional search firms are efficient for patent literature. Lawyers should run, or at least supervise, the qualification and proof steps, because those decisions are legal. The Patent Litigation Toolkit: A Roadmap and Research Guide lists research sources by phase of the case.

Step 3: Search the patent literature

Patent documents are the easiest art to qualify, because their dates and contents prove themselves, and they are the only art (along with printed publications) usable at the Board. Search them first and search them thoroughly.

1. Mine the patent's own file. Read the references cited on the face of the patent, the examiner's search notes, and every office action. Then read the file histories of family members, foreign counterparts, and any related IPRs or reexaminations. A European search report that marks a reference "X" (relevant alone) or "Y" (relevant in combination) is a free lead, and art another defendant used in an earlier challenge is a head start (and a warning about what has already failed).
2. Run the free databases. The USPTO's Patent Public Search, Google Patents, the EPO's Espacenet, and WIPO's PATENTSCOPE together cover most of the world's patent documents; national tools such as J-PlatPat (Japan) and the Chinese and Korean office databases fill gaps and offer better translations. Commercial platforms add semantic search, better family grouping, and citation analytics.
3. Combine classification and keywords. Start with CPC groups from your plan, then add keywords within those groups. Searching keywords alone across all classes buries you in noise; searching classes alone misses art that was classified elsewhere.
4. Chase citations both ways. Backward citations (what the good references cite) and forward citations (what later cites them) are often more productive than any query. Track the chain in your search log.
5. Search people and companies. Inventor and assignee searches catch the patent owner's earlier filings (which may be prior art against later claims) and competitors' work in the same years.
6. Check family members for better dates and better text. A foreign family member may have published earlier than the U.S. member, or may contain figures or examples the U.S. version dropped.

For U.S. patents and published applications relied on as § 102(a)(2) art under the AIA, collect the priority documents too. The reference is prior art as of the date its earliest application describes the relied-on subject matter, and patent owners still argue that the priority application must also support a claim of the reference, the pre-AIA rule of Dynamic Drinkware, LLC v. National Graphics, Inc., 800 F.3d 1375 (Fed. Cir. 2015). Chart the priority document as well as the reference, and you will not be caught short.

Step 4: Search the non-patent literature and the archived web

Non-patent literature (NPL) is where the best art often hides and where most qualification fights happen.

• Scholarly and technical sources. Journal databases in the field (IEEE Xplore, the ACM Digital Library, PubMed, and the major publisher platforms), conference proceedings, dissertations and theses, technical reports, and preprint servers.
• Standards and specifications. Standards bodies publish drafts, contributions, and meeting reports with dates. Remember that a standard compiled from many separately authored documents is not one reference; in Kyocera Wireless Corp. v. International Trade Commission, 545 F.3d 1340 (Fed. Cir. 2008), the GSM standard was publicly accessible but could not anticipate as a single reference because its specifications were separate documents by different authors at different times.
• Government sources. Regulatory filings and agency publications often contain dated technical descriptions: device clearance summaries, equipment authorization filings with photographs and manuals, environmental permits, grant reports, and agency advisory committee materials like those held to be printed publications in Jazz Pharmaceuticals, Inc. v. Amneal Pharmaceuticals, LLC, 895 F.3d 1347 (Fed. Cir. 2018).
• Commercial literature. Product catalogs, data sheets, application notes, user manuals, trade magazine articles, and trade show materials. A catalog distributed at a dealer trade show was a printed publication as a matter of law in GoPro, Inc. v. Contour IP Holding LLC, 908 F.3d 690 (Fed. Cir. 2018), and a product manual that anyone interested in the product could get on request (the product had about a dozen customers), dated by its inscription and backed by dated advertisements, was prior art in In re Enhanced Security Research, LLC, 739 F.3d 1347 (Fed. Cir. 2014).
• The archived web. The Internet Archive's Wayback Machine stores dated captures of web pages and many linked files. Search the patent owner's and competitors' domains, product support pages, and download directories, and record the capture URLs, which encode the capture date and time. Archived newsgroup and mailing list posts, code repositories with commit histories, and old forum threads are also fair game; a newsgroup post was publicly accessible in Suffolk Technologies, LLC v. AOL Inc., 752 F.3d 1358 (Fed. Cir. 2014).
• Library catalogs. WorldCat and individual library catalogs show whether and when a book, thesis, or report was cataloged and shelved, which is often the best proof of accessibility and date.

As you collect NPL, record for each item where you found it, how a person in the field would have found it then, and every date indication on it. Those notes become your qualification evidence in Step 6.

Step 5: Investigate products and the patent owner's own history

Products and pre-filing commercial activity cannot be used at the Board, but in court they are often the strongest art, and IPR estoppel does not reach them, Ingenico Inc. v. IOENGINE, LLC, 136 F.4th 1354 (Fed. Cir. 2025).

The patent owner's history. Build a timeline of the patent owner's product development from public sources and, once discovery opens, from its files:

1. Press releases, launch announcements, investor presentations, and securities filings that mention the product or technology.
2. Trade show appearances (exhibitor lists, booth photos, brochures, conference programs, session recordings).
3. Crowdfunding pages, preorder pages, early app store listings, and archived product pages.
4. The first quote, the first purchase order, the first shipment, and the first paid pilot, by product version.
5. Beta programs and evaluation agreements, with the actual terms: who controlled the units, whether money changed hands, and what confidentiality applied.
6. Supply and manufacturing contracts, including who held title (The Medicines Co. v. Hospira, Inc., 827 F.3d 1363 (Fed. Cir. 2016) (en banc)) and whether the patent owner itself bought commercial quantities from a supplier.

Each event is then tested against the doctrine. A demonstration of working units to the trade without confidentiality is a public use under Minerva Surgical, Inc. v. Hologic, Inc., 59 F.4th 1371 (Fed. Cir. 2023). A commercial offer of a product ready for patenting is an on-sale event under Pfaff v. Wells Electronics, Inc., 525 U.S. 55 (1998), even if confidential under Helsinn Healthcare S.A. v. Teva Pharmaceuticals USA, Inc., 586 U.S. 123 (2019). Performing a claimed method for a paying customer puts the method on sale, as in Quest Integrity USA, LLC v. Cokebusters USA Inc., 924 F.3d 1220 (Fed. Cir. 2019). And a deal the inventors privately regarded as a test is still a sale if the contract reads like one: in Sunoco Partners Marketing & Terminals L.P. v. U.S. Venture, Inc., 32 F.4th 1161 (Fed. Cir. 2022), the court looked past the inventors' stated experimental intent to the commercial terms, rejected the experimental-use negation, and sent the case back on whether the invention was ready for patenting.

Third-party products. Buy old units (online auction and surplus listings are a surprisingly good source), photograph them, and have an engineer perform and document a teardown. Record date codes, firmware versions, part numbers, labels, and packaging. Locate the sellers, distributors, and long-time customers who can testify to when the product was sold and how it was configured. Third-party software products can be dated by release notes, archived download pages, and catalog listings; in In re Epstein, 32 F.3d 1559 (Fed. Cir. 1994), abstracts that were not themselves prior art were sufficient evidence, in prosecution, that the products they described had been released or installed before the critical date.

Remember what does not count. A third party's secret use is not prior art against another inventor, W.L. Gore & Associates, Inc. v. Garlock, Inc., 721 F.2d 1540 (Fed. Cir. 1983), and a third party's use under circumstances of confidentiality may not be public, Dey, L.P. v. Sunovion Pharmaceuticals, Inc., 715 F.3d 1351 (Fed. Cir. 2013). A defendant that has been practicing in secret may instead have a prior commercial use defense under 35 U.S.C. § 273, which is a defense, not an invalidity theory, and has its own proof requirements.

Step 6: Qualify each reference

Every candidate goes through the same five questions, and the answers go in writing in a qualification memo (the companion Prior Art Qualification Checklist: A Practical Checklist turns them into a form).

Question 1: Which category is it? Patent, printed publication, public use, sale, other public availability, or § 102(a)(2) earlier-filed application. The category determines the proof and the forum.

Question 2: What is its date, and how will I prove it? For a patent, the publication or grant date (and for § 102(a)(2), the effective filing date). For a document, the date it became publicly accessible, which is not necessarily the date printed on it. A copyright year, an ISBN, a library receipt stamp, a catalog record, a conference date, or an archive capture can each help, and courts look at the whole picture; in VidStream LLC v. Twitter, Inc., 981 F.3d 1060 (Fed. Cir. 2020), a book's copyright page, ISBN, and Copyright Office and library records together established its date. For a use or a sale, the date of the earliest qualifying event.

Question 3: Was it public enough? For documents, the test is public accessibility: whether a person interested and ordinarily skilled in the subject matter, exercising reasonable diligence, could have located it. The cases give a working vocabulary:

Once accessibility is shown, nobody has to prove that a particular person actually read the document, Constant v. Advanced Micro-Devices, Inc., 848 F.2d 1560 (Fed. Cir. 1988), and a limited distribution to interested members of the art can be enough, Samsung Electronics Co. v. Infobridge Pte. Ltd., 929 F.3d 1363 (Fed. Cir. 2019). For uses and sales, the questions are different: was the use non-confidential, or was there a commercial offer, and was the invention ready for patenting?

Question 4: What exactly does it disclose, and is it enabling? Anticipation requires every element, arranged as claimed, in a single reference, expressly or inherently, Verdegaal Bros., Inc. v. Union Oil Co. of California, 814 F.2d 628 (Fed. Cir. 1987). Inherency requires that the missing element be necessarily present, not merely probably present, Continental Can Co. USA, Inc. v. Monsanto Co., 948 F.2d 1264 (Fed. Cir. 1991). The reference must enable the skilled artisan to make the claimed subject matter, though it need not prove that it works, In re Gleave, 560 F.3d 1331 (Fed. Cir. 2009).

Question 5: Does an exception remove it? Under the AIA, check whether the reference is the inventor's own disclosure within the year before filing, was derived from the inventor, follows an earlier public disclosure by the inventor of the same subject matter, or (for § 102(a)(2) art) was commonly owned with the claimed invention. After Sanho Corp. v. Kaijet Technology International Ltd., 108 F.4th 1376 (Fed. Cir. 2024), a private sale by the inventor is not the kind of "public" disclosure that shields against intervening art. Under pre-AIA law, check whether the patent owner can antedate the reference with corroborated evidence of earlier invention.

Step 7: Prove it: authentication, dates, and corroboration

A reference that cannot be admitted is not prior art in any practical sense. Build the proof as you find the art, not after expert reports are due.

Documents. Authenticate under Fed. R. Evid. 901 through a witness with knowledge (an author, a librarian, a publisher's records custodian), distinctive characteristics, comparison with an authenticated copy (the route approved in Valve Corp. v. Ironburg Inventions Ltd., 8 F.4th 1364 (Fed. Cir. 2021)), or the ancient-documents provision for documents at least 20 years old. Use self-authentication under Fed. R. Evid. 902 where available, including certified business records and certified electronic records. Declarations can be made under penalty of perjury without a notary under 28 U.S.C. § 1746.

Dates and hearsay. The content of a reference is not hearsay when offered for what it discloses. A printed date offered to prove the publication date can be, so plan a route: the ancient-documents exception in Fed. R. Evid. 803(16) for documents prepared before 1998, business-records foundations under Rule 803(6), public records under Rule 803(8), or the residual exception in Fed. R. Evid. 807. At the Board, the Federal Rules of Evidence apply under 37 C.F.R. § 42.62, objections must be made within the short periods set by 37 C.F.R. § 42.64 or are waived, and the Board may let a petitioner answer a challenge to a reference's date with additional evidence; in VidStream the petitioner answered the challenge with a Library of Congress copy, the Copyright Office registration, and a library-cataloging expert's declaration, and the court approved the Board's decision to consider them.

Archived web pages. Request an affidavit from the Internet Archive's records custodian attesting to the captures (the Archive publishes its procedure and fee), and look for independent confirmation: a second copy from another source, a dated citation in another document, a contemporaneous email attaching the file, or a witness who downloaded it. Capture the page yourself in a forensically sound way, preserving the full capture URL and the HTTP headers. Note the date of the capture of the file you rely on, not just the page that linked to it, and check whether the file changed between captures. Authenticating Website Evidence: A Practical Checklist and Capturing the Web: A Practitioner's Guide to Authenticating Website Screenshots as Evidence in Federal Court cover the mechanics.

Testimony about uses and sales. Oral testimony about a prior use or sale must be corroborated, whether the witness is interested (Woodland Trust v. Flowertree Nursery, Inc., 148 F.3d 1368 (Fed. Cir. 1998)) or not (Finnigan Corp. v. International Trade Commission, 180 F.3d 1354 (Fed. Cir. 1999)). Contemporaneous documents are the preferred corroboration, Juicy Whip, Inc. v. Orange Bang, Inc., 292 F.3d 728 (Fed. Cir. 2002), evaluated under a rule of reason that weighs all the evidence, Sandt Technology, Ltd. v. Resco Metal & Plastics Corp., 264 F.3d 1344 (Fed. Cir. 2001). Interview witnesses early, before memories are shaped by the litigation, and collect their documents at the same time.

Physical products. Keep a chain of custody from acquisition through teardown and trial. Photograph and video every step, keep the units, and have the person who did the teardown prepared to testify. Tie the unit to the critical date with date codes, purchase records, and configuration evidence, and be ready to show that the unit was not modified after sale.

Evidence held abroad. Foreign companies' records and witnesses may need to be reached through the Hague Evidence Convention or letters of request, which take months; depositions abroad must be arranged under Fed. R. Civ. P. 28(b). Start early; see the Cross-Border Discovery Toolkit: 1782 Applications, Hague Requests, and Blocking Statute Analyses.

Step 8: Chart it

The claim chart is where prior art becomes an argument. Courts, the Board, and opposing experts read charts closely, and a careless chart undermines a good reference.

1. One row per claim element, using the exact claim language and your lettering from Step 1.
2. Pinpoint citations to the reference (page, column and line, paragraph, figure, and reference numeral), with the quoted text in the cell. Never paraphrase the reference in the chart itself.
3. Construction notes where the mapping depends on a construction, with the alternative mapping under the other side's construction.
4. Inherency support where an element is not express: the expert's explanation of why it is necessarily present, with test data if possible.
5. Enablement note for anything a patent owner may attack as a non-enabling disclosure.
6. For obviousness, a combination chart showing which reference supplies each element, plus a separate statement of the reason a skilled artisan would have combined them with a reasonable expectation of success under KSR International Co. v. Teleflex Inc., 550 U.S. 398 (2007), and an inventory of the objective indicia the patent owner is likely to raise under Graham v. John Deere Co., 383 U.S. 1 (1966).

Do not stitch multiple documents together and call the result anticipation. Separate documents are separate references unless one incorporates the other by specific reference (Kyocera), and elements drawn from different embodiments of one reference are an obviousness argument unless the reference directs the combination, Net MoneyIN, Inc. v. VeriSign, Inc., 545 F.3d 1359 (Fed. Cir. 2008). Templates for anticipation and obviousness charts are in the Prior Art Toolkit: Search Protocols, Invalidity Charts, and On-Sale Bar Investigations.

Step 9: Use it in prosecution and post-grant examination

Prior art reaches the Patent Office through four doors: the applicant's information disclosure statement (IDS), a third party's preissuance submission, a citation placed in an issued patent's file, and a request for reexamination. Each has its own deadline and its own consequences.

If you are the applicant, disclose on time and in usable form. The duty of candor in 37 C.F.R. § 1.56 binds each inventor, each attorney or agent, and everyone else substantively involved in the application until the patent issues. There is no general duty to search, FMC Corp. v. Hennessy Industries, Inc., 836 F.2d 521 (Fed. Cir. 1987), but material information those people know must go in, including the company's own demonstrations, pilots, and early sales. Timing is set by 37 C.F.R. § 1.97, and MPEP § 609 explains the practice:

The § 1.97(e) statement is available only if each item was first cited by a foreign patent office in a counterpart application within the preceding three months, or if nobody with the duty knew of it more than three months earlier, so docket a three-month clock from every foreign search report and every internal discovery. Under 37 C.F.R. § 1.98, supply legible copies of everything except U.S. patents and published applications, and for a non-English document a concise explanation of relevance plus any translation already in hand. Do not trim the explanation to the helpful parts: in Semiconductor Energy Laboratory Co. v. Samsung Electronics Co., 204 F.3d 1368 (Fed. Cir. 2000), a 29-page Japanese reference filed with an accurate but incomplete one-page translation that left out its most material teaching supported a judgment of unenforceability. That case predates the stricter intent standard of Therasense, Inc. v. Becton, Dickinson & Co., 649 F.3d 1276 (Fed. Cir. 2011) (en banc), but the drafting lesson stands. Citing a reference is not an admission that it is material (37 C.F.R. § 1.97(h)). The routine is set out in Maintaining the Duty of Candor to Avoid Inequitable Conduct: A Practical Checklist.

Remove what can be removed. When the examiner rejects over the inventor's own disclosure within the grace year, or over a third party's disclosure that followed the inventor's public disclosure of the same subject matter, answer with a declaration under 37 C.F.R. § 1.130 (MPEP § 2155) built from documents: the earlier disclosure itself, dated drafts and emails, and an explanation for any co-author who is not a named inventor. For pre-AIA applications, a declaration under 37 C.F.R. § 1.131 antedates a reference with corroborated proof of earlier invention (MPEP § 715). Neither can remove a disclosure made more than a year before filing. If a competitor's application claims what it took from your inventor, the remedy is a derivation proceeding under 35 U.S.C. § 135, petitioned within one year after the competitor's claim is first published. Rejection strategy generally is covered in Responding to a Patent Office Action: A Practical Checklist.

If you are watching a competitor's application. Anyone may file printed publications in a pending application under 35 U.S.C. § 122(e) and 37 C.F.R. § 1.290, before the earlier of allowance and the later of six months after publication or the first rejection. Each document needs a concise description of its relevance, a first submission of three or fewer documents is free with the required statement, and the submitter need not name the real party in interest (MPEP § 1134). Weigh what you give up. Art the examiner has considered loses the jury instruction available for art the Office never saw (Step 10), and a later petition on the same art invites discretionary denial under 35 U.S.C. § 325(d). Submit when narrower claims now are worth more than a fresh reference later.

After the patent issues. Any person may cite patents and printed publications in the patent's file under 35 U.S.C. § 301, together with the patent owner's own statements about claim scope made in court or in the Office, and may ask that its identity be kept confidential; those statements can later be used to construe the claims in reexamination or a Board trial. The stronger tool is ex parte reexamination under 35 U.S.C. § 302 and 37 C.F.R. § 1.510, which requires applying the cited art to every challenged claim:

1. The Office decides within three months whether the request raises a substantial new question of patentability (35 U.S.C. § 303), and it can find one even on art it considered before, In re Swanson, 540 F.3d 1368 (Fed. Cir. 2008).
2. The patent owner may file a statement and the requester a reply (35 U.S.C. § 304); after that the requester drops out, and examination proceeds between the owner and the examiner (35 U.S.C. § 305), with no broadening amendments.
3. Amended or new claims carry intervening rights for those already practicing them (35 U.S.C. § 307(b)).
4. There is no estoppel, and a court's earlier refusal to invalidate does not bind the Office, which applies a lower burden, In re Baxter International, Inc., 678 F.3d 1357 (Fed. Cir. 2012). A cancellation that becomes final while an infringement case is still pending ends that case, even after a trial win, Fresenius USA, Inc. v. Baxter International, Inc., 721 F.3d 1330 (Fed. Cir. 2013).

If you own the patent, repair it before someone else finds the problem. Supplemental examination under 35 U.S.C. § 257 lets the Office consider newly found information and generally bars a later unenforceability claim based on it, unless the claim was pleaded before the request. Reissue under 35 U.S.C. § 251 narrows claims around art (broadening only within two years of grant), and 35 U.S.C. § 253 lets the owner disclaim claims it cannot defend. Every repair is cheaper before a defendant serves contentions. The procedures are compared in Patent Post-Grant Proceedings: IPR, PGR, and Reexamination at the PTAB.

Step 10: Use it in district court

In court, a reference has to clear a series of deadlines before anyone weighs it. Miss one and good art can be excluded without a ruling on the merits.

1. Plead it twice. Assert invalidity as a defense under 35 U.S.C. § 282(b) and as a counterclaim for a declaratory judgment under 28 U.S.C. § 2201 and Fed. R. Civ. P. 13. Plead facts, because courts increasingly test counterclaims (and, in many districts, defenses) for plausibility, and plead any inequitable conduct with the particularity Exergen Corp. v. Wal-Mart Stores, Inc., 575 F.3d 1312 (Fed. Cir. 2009), requires. One trap: your own declaratory judgment action challenging validity, filed before an IPR petition, bars the petition, although a counterclaim does not (35 U.S.C. § 315(a)(1), (a)(3)). The pleading choices are covered in Drafting an Answer and Affirmative Defenses: A Practical Guide.
2. Preserve early. Put your own engineering history under a litigation hold, demand that the patent owner preserve its pre-filing product, marketing, and sales records, and subpoena prior artists before their files age out; a nonparty generally has no duty to preserve until served. See the Litigation Hold and Evidence Preservation Checklist: A Practical Checklist.
3. Serve complete contentions on schedule. Under local patent rules such as N.D. Cal. Patent L.R. 3-3 and 3-4 and E.D. Tex. P.R. 3-3 and 3-4, invalidity contentions typically come due about 45 days after the infringement contentions and must identify each item of art (for a prior sale or use, the item, the date, and the people involved), chart every element, state the combinations and reasons to combine, and produce the art. Elsewhere, interrogatories under Fed. R. Civ. P. 33 and the Fed. R. Civ. P. 16 scheduling order do the same work. Amendment requires good cause, which means diligence, O2 Micro International Ltd. v. Monolithic Power Systems, Inc., 467 F.3d 1355 (Fed. Cir. 2006), and undisclosed theories can be excluded under Fed. R. Civ. P. 37(c)(1). Expect the court to make you narrow to a handful of references before trial.
4. Aim discovery at qualification. From the patent owner, use document requests under Fed. R. Civ. P. 34, a Fed. R. Civ. P. 30(b)(6) deposition on the first offer, sale, demonstration, and publication of each product version, and requests under Fed. R. Civ. P. 36 to admit the genuineness and dates of its brochures, manuals, and web pages; an admission ends an authentication fight before it starts. From third parties, serve a document subpoena under Fed. R. Civ. P. 45 first and a deposition subpoena second, within 100 miles of where the witness works. The Nonparty Discovery Toolkit: Subpoenas, Third-Party Records, and Privilege and Preparing and Defending a Rule 30(b)(6) Deposition cover the mechanics.
5. Write expert reports for a hostile reader. A report under Fed. R. Civ. P. 26(a)(2)(B) must state every opinion and its basis. Anticipation testimony must come from someone skilled in the art, identify each element, and explain in detail where the reference discloses it, Schumer v. Laboratory Computer Systems, Inc., 308 F.3d 1304 (Fed. Cir. 2002); Koito Manufacturing Co. v. Turn-Key-Tech, LLC, 381 F.3d 1142 (Fed. Cir. 2004). An obviousness opinion that lists references without saying how or why a skilled artisan would combine them can be excluded, Innogenetics, N.V. v. Abbott Laboratories, 512 F.3d 1363 (Fed. Cir. 2008), and a patent lawyer without expertise in the art may not testify on invalidity at all, Sundance, Inc. v. DeMonte Fabricating Ltd., 550 F.3d 1356 (Fed. Cir. 2008). Since the 2023 amendment, Fed. R. Evid. 702 makes the proponent show reliability by a preponderance. See Taking and Defending an Expert Deposition: A Practical Guide.
6. Move for summary judgment only on a documentary record. The clear-and-convincing burden applies at summary judgment, Anderson v. Liberty Lobby, Inc., 477 U.S. 242 (1986), so the best motions rest on papers nobody disputes: signed purchase orders before the critical date, a cataloged thesis, an anticipation case that turns on claim construction. Disputes about accessibility or a witness's credibility usually go to trial, as in SRI International. See Summary Judgment Under Rule 56: Winning and Surviving Before Trial.
7. Give notice, then try it. Serve the § 282(c) notice at least 30 days before trial, listing every patent and publication and the name and address of every person who may testify to prior knowledge, use, or sale; without it, the proof can be excluded. The challenger must prove invalidity by clear and convincing evidence even for art the examiner never saw, but may ask the court to tell the jury that the Office had no chance to consider it, Microsoft Corp. v. i4i Ltd. Partnership, 564 U.S. 91 (2011); the burden does not rise when the examiner did see it, Sciele Pharma Inc. v. Lupin Ltd., 684 F.3d 1253 (Fed. Cir. 2012). Jurors remember the engineer who built the old device and the device itself far better than any chart. Move under Fed. R. Civ. P. 50(a) before the case goes to the jury, or the post-trial motion is lost; see Filing or Opposing Post-Trial Motions Under Rules 50, 59, and 60: A Practical Guide.

The same art and proof rules apply in a Section 337 investigation at the International Trade Commission, where every legal and equitable defense is available (19 U.S.C. § 1337(c)) on a schedule measured in months rather than years.

Step 11: Use it at the Patent Trial and Appeal Board

The Board offers technically trained judges, a fixed schedule, and a lower burden: a preponderance of the evidence (35 U.S.C. § 316(e)). In exchange it narrows what you can use and charges for the privilege in estoppel.

1. Choose the proceeding. Inter partes review takes only §§ 102 and 103 grounds based on patents and printed publications and opens nine months after grant (35 U.S.C. § 311(b)-(c)). Post-grant review takes any invalidity ground, including public use and sale, but only within nine months of grant of an AIA patent (35 U.S.C. § 321(c)) and only if unpatentability is more likely than not (35 U.S.C. § 324(a)).
2. Make sure every ground rests on qualifying art. The patent's own description of the prior art is not a "patent or printed publication," Qualcomm Inc. v. Apple Inc., 24 F.4th 1367 (Fed. Cir. 2022). It may show general knowledge, but a petition that lists it as part of the basis of a ground violates § 311(b) even when real references are combined with it, Qualcomm Inc. v. Apple Inc., 134 F.4th 1355 (Fed. Cir. 2025). A published U.S. application counts as a printed publication as of its filing date when the statute makes it prior art as of that date, Lynk Labs, Inc. v. Samsung Electronics Co., No. 2023-2346 (Fed. Cir. Jan. 14, 2025). Manuals, catalogs, and archived pages qualify only with proof of public accessibility.
3. Calendar the deadlines. A petition filed more than one year after the petitioner, a real party in interest, or a privy was served with an infringement complaint is barred (35 U.S.C. § 315(b)), and the Board's time-bar ruling cannot be appealed, Thryv, Inc. v. Click-To-Call Technologies, LP, 590 U.S. 45 (2020). The patent owner's preliminary response under 35 U.S.C. § 313 is due three months after the petition receives a filing date (37 C.F.R. § 42.107(b)), institution is decided within three months after that (35 U.S.C. § 314(b)), and the final written decision follows within a year of institution, appealable under 35 U.S.C. § 319.
4. Put the whole case in the petition. It must identify each claim, each ground, the claim constructions, and where every element appears, with exhibit citations (35 U.S.C. § 312(a)(3); 37 C.F.R. § 42.104(b)), in 14,000 words (37 C.F.R. § 42.24). A petitioner cannot rebuild its case in reply, Intelligent Bio-Systems, Inc. v. Illumina Cambridge Ltd., 821 F.3d 1359 (Fed. Cir. 2016), and the Board may not fill gaps with arguments the petitioner never made, In re Magnum Oil Tools International, Ltd., 829 F.3d 1364 (Fed. Cir. 2016). Support the reason to combine with evidence, Personal Web Technologies, LLC v. Apple, Inc., 848 F.3d 987 (Fed. Cir. 2017), and do not ask "common sense" to supply a missing element, Arendi S.A.R.L. v. Apple Inc., 832 F.3d 1355 (Fed. Cir. 2016). Expert testimony that does not disclose its underlying facts or data gets little or no weight (37 C.F.R. § 42.65(a)).
5. File the accessibility proof with the petition. At institution the petitioner must show a reasonable likelihood that a reference was publicly accessible, judged on the totality of the evidence, under the Board's precedential decision in Hulu, LLC v. Sound View Innovations, LLC, IPR2018-01039, Paper 29 (P.T.A.B. Dec. 20, 2019). Exhibit the archive affidavit, library declarations, and catalog records up front, with a translation and accuracy affidavit for any foreign document (37 C.F.R. § 42.63(b)). Objections are due within ten business days of institution, and supplemental evidence within ten business days of an objection (37 C.F.R. § 42.64(b)).
6. Expect discretion. The Director may deny a petition built on art or arguments the Office already considered (§ 325(d); Advanced Bionics, LLC v. MED-EL Elektromedizinische Geräte GmbH, IPR2019-01469, Paper 6 (P.T.A.B. Feb. 13, 2020) (precedential)), or because a parallel case will reach trial first (Apple Inc. v. Fintiv, Inc., IPR2020-00019, Paper 11 (P.T.A.B. Mar. 20, 2020) (precedential)). That practice has swung several times, most sharply in 2025, when the Office withdrew guidance that had limited denials and moved discretionary questions to the Director on separate briefing. Check the current guidance before building a strategy around the Board.
7. Plan for estoppel. After a final written decision, the petitioner may not argue in court that a claim is invalid on any ground it raised or reasonably could have raised (35 U.S.C. § 315(e)(2)), including grounds left out of the petition, California Institute of Technology v. Broadcom Ltd., 25 F.4th 976 (Fed. Cir. 2022), measured by what a skilled searcher's diligent search would have found (Ironburg). Product, public use, and on-sale theories survive (Ingenico). Put your best documents in the petition, keep the product case for court, and keep the search log. The playbook for both sides is in Filing or Defending an Inter Partes Review: A Practical Guide and Inter Partes Review Strategy: Discretionary Denial, Estoppel, and the Parallel District Court Case.

Timelines and costs across forums

The AIPLA's biennial Report of the Economic Survey is the usual source for current litigation and PTAB cost benchmarks.

Step 12: How patent owners attack prior art, and how to answer

Every reference has a soft spot. The patent owner's job is to find it; the challenger's job is to have shored it up before anyone looks. The common attacks, the governing rules, and the answers:

Patent owners have procedural moves as well. At the Board, the preliminary response is the chance to contest accessibility and invoke § 325(d) and parallel-litigation discretion before institution; afterward, the owner can cross-examine the petitioner's expert and move to amend, with the petitioner bearing the burden of proving substitute claims unpatentable (37 C.F.R. § 42.121(d); see Aqua Products, Inc. v. Matal, 872 F.3d 1290 (Fed. Cir. 2017) (en banc)). In court, motions to strike late contentions, challenges under Rule 702, and motions in limine on IPR estoppel narrow the field. The cheapest defense of all is the owner's own prior art audit before suit, discussed in Do You Have to Enforce Your Patent? Duty, Demand Letters, and the Cost of Doing Nothing. For obviousness fights in particular, see Overcoming Obviousness Rejections: A Comprehensive Guide to Section 103 Analysis.

Common mistakes

• Searching before dating the claims. A search run against the wrong critical date or the wrong version of § 102 wastes the budget and misses the patent owner's own history.
• Keeping no search log. The log proves diligence when you amend contentions and shows what a skilled searcher would or would not have found when estoppel is argued.
• Treating an archive printout as proof. Without a custodian affidavit and independent corroboration, it is an invitation to exclusion.
• Charting the version you cannot date. Manuals, web pages, and firmware change; chart the version you can prove existed before the critical date.
• Subpoenaing prior artists at the end of discovery. Their records and memories are the first evidence to disappear.
• Filing your own declaratory judgment action before an IPR petition, which bars the petition under § 315(a)(1).
• Building an IPR ground on the product or on the patent's own admissions instead of on patents and printed publications.
• Leaving a reference out of the contentions or the § 282(c) notice, then trying to use it at trial.
• For applicants, the disclosure mistakes. Missing the three-month IDS clock, filing a selective translation, or keeping the company's own launch history out of the file.

Worked example: the Vortiq manual on archive.org

Halvorsen Sensing sues Copperline Instruments in the Northern District of California on its '614 patent. Claim 1 recites a portable gas monitoring system with (a) a handheld monitor with a gas sensor; (b) a docking station with a calibration gas source; (c) a controller that automatically starts a bump test when the monitor is seated in the dock; (d) wireless upload of the result to a remote server; and (e) a lockout that keeps the monitor out of measurement mode after a failed test. The patent issued from an application filed May 18, 2017, claiming a provisional filed May 19, 2016. Two weeks after service, a Copperline engineer sends the email that opens this guide.

Weeks 1 to 2: fix the target. Both candidate dates fall after March 16, 2013, so the AIA governs. Counsel charts the provisional against claim 1 and finds no lockout, so claim 1 may be entitled only to May 18, 2017. The working critical date is May 19, 2016, with the later date as a fallback.

Weeks 2 to 4: find it. Vortiq Systems was acquired by Strand Industrial in 2019, and its website is gone. The Wayback Machine holds dozens of captures of the VQ-300 support page from 2014 to 2018, each linking to "VQ300_UserManual_RevC.pdf," and the PDF itself was first captured on March 3, 2015. Revision C describes a dock with a replaceable calibration gas cylinder, cellular upload to the VortiqCloud portal, and a "FAIL" lockout. The team also finds the VQ-300's FCC equipment authorization file, which contains a user manual exhibit, and buys two used monitors and a dock at online auction.

Weeks 3 to 6: qualify it. The manual sat on an unrestricted support page linked from the product page of a company in the field, and it shipped with every unit, like the manuals in Weber. The date has a cushion of more than a year: any public availability before May 19, 2016 suffices, and no § 102(b) exception can apply to a third party's disclosure made more than a year before the effective filing date. Element (c) is the weak point. Revision C says the dock "runs the scheduled bump test when the monitor is seated," and Halvorsen will argue that a scheduled test is not one started by seating. Counsel charts the manual under both constructions and adds an obviousness combination with a 2013 published application from another company that describes a dock starting calibration on insertion. The FCC exhibit turns out to be Revision A, which lacks the cloud upload, and the file shows a confidentiality request that delayed its public release, so it stays in the file as corroboration, not as a ground.

Months 2 to 6: prove it. Counsel orders an Internet Archive affidavit for the page and PDF captures; serves Strand with a document subpoena for revision history, web posting records, and sales records, followed by a deposition subpoena; finds Vortiq's former technical writer, who remembers posting Revision C and still has the source files; and locates a water utility whose safety binder holds a printed Revision C next to an April 2015 purchase order. The utility's copy matches the archived PDF page for page, the comparison route of Valve. The teardown expert documents late-2014 date codes, the firmware version, and the decisive fact: the dock starts a bump test the moment a monitor is seated whenever one is due.

Months 4 to 7: deploy it. The invalidity contentions chart the manual (anticipation under both constructions, plus the combination), the VQ-300 system as public use and on-sale art, and the utility's purchase as a dated sale. Well inside the one-year bar, Copperline petitions for inter partes review on the manual and the 2013 application, keeps the product theories for court because they survive estoppel, and moves to stay the case.

Halvorsen's side. Its preliminary response calls the support page obscure and the capture unreliable, and after institution it objects to the capture's authenticity; the affidavit, the utility's matching copy, and the writer's declaration answer both. Its real fight is element (c), so it presses a construction requiring that seating alone trigger the test. That creates a squeeze: if its infringement theory reads "automatically" to cover Copperline's scheduled tests, the same reading reads on Vortiq. Halvorsen's better assets are dependent claims reciting features Vortiq never had, such as claim 9's temperature-compensated sensor curve. The lesson for patent owners is to run this search before suing and, if it turns up a Vortiq, to narrow the patent by reissue or reexamination while the choice is still theirs.

Frequently asked questions

Is a Wayback Machine printout enough to prove when a page was public? Rarely on its own. Many courts and Board panels accept an Internet Archive custodian affidavit as proof of what the Archive captured and when, but the patent owner can still argue that nobody could have found the page, that the linked file is a different version, or that the date is hearsay. Pair the affidavit with something independent: a dated copy from another source, a witness who used the page, or the publisher's own records.

Can a product manual support an inter partes review? Yes, as a printed publication, if you can prove it was publicly accessible before the critical date (Weber; GoPro). The product itself cannot be the basis of an IPR ground, which is why product-based public use and on-sale theories survive IPR estoppel (Ingenico).

Our best reference is in Japanese. What do we need? Machine translation is fine for screening. For anything you rely on, get a certified translation: the Board requires a translation and an affidavit attesting to its accuracy (37 C.F.R. § 42.63(b)), a court will want a translator who can testify, and an IDS needs a concise explanation of relevance (37 C.F.R. § 1.98(a)(3)). Never file a selective translation (Semiconductor Energy Laboratory).

Do we have to tell the Patent Office about art from our own freedom-to-operate search? If the art is material to claims in your own pending applications and someone with the duty knows of it, yes. There is no duty to search (FMC), but there is no license to ignore what a search turned up. The opinion analyzing another company's patent is a different matter and usually stays privileged; see Conducting Freedom-to-Operate Analysis for New Products.

Should we show the patent owner our prior art before it sues? Sometimes. Strong art can end a demand campaign, can support a fee request under 35 U.S.C. § 285 if the owner sues anyway, and a well-founded invalidity analysis made at the time can bear on willfulness under Halo Electronics, Inc. v. Pulse Electronics, Inc., 579 U.S. 93 (2016). But a belief that the patent is invalid is no defense to induced infringement, Commil USA, LLC v. Cisco Systems, Inc., 575 U.S. 632 (2015), and showing your hand lets the owner repair the patent or draft continuation claims around your art. The inducement side is covered in Pleading and Proving Induced and Contributory Patent Infringement: A Practical Guide.

We found better art after our contentions were due. Can we still use it? Move promptly to amend and prove diligence: when you searched, what you found, and why a reasonable search would not have turned this up sooner (O2 Micro). If an IPR you filed has reached a final written decision and the new art is a patent or publication, expect the patent owner to argue that a skilled searcher would have found it; Ironburg puts that burden on the owner, but your search log is the best answer. Either way, list it in the § 282(c) notice.

What happens if the Board and the court disagree? The first final answer of invalidity usually wins. A Federal Circuit affirmance of a Board unpatentability decision binds the patent owner in every pending case, XY, LLC v. Trans Ova Genetics, L.C., 890 F.3d 1282 (Fed. Cir. 2018), and a cancellation that becomes final before the infringement judgment does ends the case (Fresenius). A court's earlier refusal to invalidate does not bind the Board, which applies a lower burden and may have a different record, Novartis AG v. Noven Pharmaceuticals Inc., 853 F.3d 1289 (Fed. Cir. 2017).

Practical takeaways

• Date every claim and choose the statute before the first search.
• Search patents, non-patent literature, and products, starting with the patent owner's own history, and log every search.
• Qualify each candidate in writing: category, date, accessibility, content, enablement, and exceptions.
• Build the proof as you find the art: affidavits, custodians, corroborating documents, and chain of custody.
• Chart element by element with pinpoint citations, and plead obviousness in the alternative.
• Match the art to the forum: documents to the Board under a preponderance standard, products and sales to court; calendar the one-year bar and plan for estoppel.
• Meet every disclosure deadline: contentions, expert reports, and the § 282(c) notice.
• Patent owners: disclose your own history, watch the three-month IDS clock, and audit before you sue.

This document is general information, not legal advice for any particular situation; the law changes, and the facts matter.

Related Documents

Related Articles

• Prior Art Under the America Invents Act: Section 102, the On-Sale Bar, Public Use, and the One-Year Grace Period: the doctrine behind every step of this guide.
• Inter Partes Review Strategy: Discretionary Denial, Estoppel, and the Parallel District Court Case: forum choice for challengers holding both paper and product art.
• Patent Post-Grant Proceedings: IPR, PGR, and Reexamination at the PTAB: the administrative routes compared.
• Inequitable Conduct in Patent Prosecution: Navigating the Atomic Bomb of Patent Law: what withholding material art costs.
• Claim Construction and Markman Hearings: How Courts Decide What a Patent Actually Covers: the constructions every chart depends on.
• Overcoming Obviousness Rejections: A Comprehensive Guide to Section 103 Analysis: combinations, motivation, and objective indicia.
• Conducting Freedom-to-Operate Analysis for New Products: searching before launch rather than after suit.
• Summary Judgment Under Rule 56: Winning and Surviving Before Trial: when a documentary invalidity record can end the case.

Related Guides

• Filing or Defending an Inter Partes Review: A Practical Guide: petitions, preliminary responses, and trial at the Board.
• Drafting an Answer and Affirmative Defenses: A Practical Guide: pleading invalidity defenses and counterclaims.
• Taking and Defending an Expert Deposition: A Practical Guide: preparing and attacking invalidity experts.
• Pleading and Proving Induced and Contributory Patent Infringement: A Practical Guide: the infringement claims that invalidity defenses usually answer.
• Filing or Opposing Post-Trial Motions Under Rules 50, 59, and 60: A Practical Guide: preserving an invalidity verdict or attacking one.
• Capturing the Web: A Practitioner's Guide to Authenticating Website Screenshots as Evidence in Federal Court: the evidence law behind archived pages.
• Preparing and Defending a Rule 30(b)(6) Deposition: corporate testimony about launches and first sales.

Related Checklists

• Prior Art Qualification Checklist: A Practical Checklist: the reference-by-reference qualification form.
• Authenticating Website Evidence: A Practical Checklist: foundation steps for archived pages and screenshots.
• Maintaining the Duty of Candor to Avoid Inequitable Conduct: A Practical Checklist: IDS practice for applicants.
• Responding to a Patent Office Action: A Practical Checklist: answering anticipation and obviousness rejections.
• Litigation Hold and Evidence Preservation Checklist: A Practical Checklist: preserving product history before it disappears.

Related Toolkits

• Prior Art Toolkit: Search Protocols, Invalidity Charts, and On-Sale Bar Investigations: search logs, chart templates, and discovery requests.
• Patent Litigation Toolkit: A Roadmap and Research Guide: research sources by phase of the case.
• Nonparty Discovery Toolkit: Subpoenas, Third-Party Records, and Privilege: subpoenas to prior artists and distributors.
• Cross-Border Discovery Toolkit: 1782 Applications, Hague Requests, and Blocking Statute Analyses: reaching prior art evidence held abroad.