Non-patent literature: prior art that isn't a patent
What counts as a printed publication, the main types of non-patent literature, how to date it, and why it decides what can be argued at the PTAB.
By the One Transform team6 min read
Non-patent literature (NPL) is any prior art that is not a patent or a published patent application: journal and conference papers, theses, standards, product manuals and datasheets, archived web pages, source code releases and presentations. In US practice, a document of this kind is prior art as a printed publication if it was publicly accessible before the critical date, meaning that people interested and ordinarily skilled in the field, exercising reasonable diligence, could have found it. NPL matters because the earliest description of a technology is often outside the patent record, and because at the PTAB it is one of only two kinds of evidence a petition can rest on.
What makes a document a printed publication
Under 35 U.S.C. § 102(a)(1), a claimed invention is not patentable if it was "described in a printed publication" before the effective filing date. The test is not about printing. It is about public accessibility: whether the document was disseminated or otherwise made available so that interested persons ordinarily skilled in the subject matter, exercising reasonable diligence, could locate it (MPEP 2128).
Two Federal Circuit cases show how far that reaches:
- In In re Hall, 781 F.2d 897 (Fed. Cir. 1986), a single doctoral dissertation, indexed and shelved in a German university library, was a printed publication once it was publicly accessible. One copy was enough.
- In In re Klopfenstein, 380 F.3d 1345 (Fed. Cir. 2004), a poster displayed for about two and a half days at a professional meeting, with no restriction on copying, was a printed publication. It was never distributed or indexed. Display to the right audience was enough.
The other side of the line matters just as much. Material shared under a confidentiality agreement, internal reports, and drafts circulated only within a closed group may not qualify. When public accessibility is in doubt, practitioners look at how widely the document was shared, whether it was indexed or catalogued, how long it was available, who the audience was, and whether anyone expected it to stay confidential.
Types of NPL and what to check for each
| Type | Where to look | How it is dated | Watch for |
|---|---|---|---|
| Journal articles | Academic indexes, publisher archives | Issue date, online publication date | Received, accepted and published dates differ |
| Conference papers and posters | Proceedings, conference websites, printed programs | Conference dates, proceedings release | Papers handed to attendees before the proceedings appeared |
| Theses and dissertations | University repositories, library catalogs | Catalog and shelving records | Embargoed theses; deposit is not the same as indexing |
| Standards and contributions | Standards bodies' document archives, meeting reports | Upload or meeting date | Member-only access can raise accessibility questions |
| Product manuals and datasheets | Manufacturer support pages, distributor archives, trade show material | Revision date, shipping records | A copyright year alone is weak evidence of a release date |
| Archived web pages | Web archives such as the Internet Archive's Wayback Machine | Capture timestamp | A capture shows the page existed then, not when it first appeared |
| Source code releases | Public repositories, release archives, mailing lists | Release or tag date, mailing-list post date | Commits made in a private repository were not public |
| Presentations and white papers | Event sites, company sites, slide archives | Event date, posting date | Whether slides were distributed or only shown |
Where to look
- Start with what is already cited. The patent and its family members often list NPL on their front pages and in foreign search reports. Each listed paper has its own reference list.
- Follow the inventors. Inventors publish papers, give talks and write theses before they file, and their co-authors often do too.
- Search the conferences of the field for the years before the filing date, including workshops and poster sessions, not only the main proceedings.
- Check standards bodies. Technical contributions to a standards working group often describe a feature years before anyone claims it.
- Find the product documentation. For any product sold in the period, look for the user manual, datasheet, application notes and marketing brochures.
- Use web archives for company product pages, documentation sites and project pages as they stood before the critical date.
- Read project histories for open-source software: release notes, tagged releases and mailing-list announcements.
Prior-art search beyond keywords covers how to find these through citation chains, classification and period-appropriate terminology, which matters most for NPL because older papers rarely use a patent's vocabulary.
Dating the evidence
A non-patent reference is only useful if you can show it was public before the critical date, and that showing is often harder than finding the document.
- Collect the date evidence when you find the document. Save the catalog record, the archive capture details, the conference program or the release page at the time, not months later when the case needs them.
- Prefer independent dates. A library catalog entry, an archive capture or a dated conference program is stronger than a date printed on the document by its author.
- Separate creation from publication. A file's internal date, a copyright line or a "last updated" footer shows when something was written, not when the public could find it.
- Plan for authentication. In litigation and at the PTAB, practitioners often support archive captures and library records with declarations from the people who keep them.
Add a "date evidence" column to your claim chart so each reference carries its proof of public availability with it.
Why NPL matters at the PTAB
Inter partes review is narrower than district court litigation. Under 35 U.S.C. § 311(b), a petitioner may request cancellation only on grounds under § 102 or § 103, and only on the basis of prior art consisting of patents or printed publications.
That has a practical consequence. Section 102(a)(1) also covers inventions "in public use, on sale, or otherwise available to the public," but those categories cannot be the basis of an IPR ground. A product that was sold before the critical date cannot itself be an IPR reference. Its user manual, if it was publicly accessible, can be. Challengers who know of an earlier product therefore look for the documents that describe it: manuals, datasheets, brochures and archived product pages. The product itself remains available as evidence in district court.
Expect the patent owner to contest whether a manual or web page was publicly accessible before the critical date. The dating evidence described above belongs in the petition from the start.
NPL also tends to be the art an examiner did not see. Patent examination searches lean on patent collections, so a conference paper or product manual is often new to the record. Once found, it is charted like any other reference and can anchor either an anticipation or an obviousness ground; anticipation vs. obviousness explains how the two differ. It is also essential in patentability and validity searches, though rarely relevant in freedom-to-operate work, a distinction set out in FTO, patentability and validity searches compared.
How One Transform covers NPL
One Transform's searches cover patents, academic literature and the open web. The Prior Art search reaches non-patent literature through academic search, conference archives and historical product documentation, alongside patent sources. Every reference is scored against the claim elements it discloses, and each finding links to its source, so the document and its date can be checked directly.
Next step
Pick a patent you are evaluating and list what a skilled person in its field was publishing and selling in the two or three years before its priority date. To search those sources alongside the patent record, start a Prior Art search from the One Transform product overview.
This article is general information about patent practice, not legal advice. For advice on a specific matter, consult a registered patent attorney or agent.
