The prior art definition sits in one section of the statute, and reading it directly answers most questions faster than any summary.
35 U.S.C. 102 has two working parts. Subsection (a) says what counts. Subsection (b) says what is taken back out.
The governing date is the effective filing date, not the date of invention. That changed with the America Invents Act for applications filed on or after 16 March 2013, and it is the single most consequential difference from the old system.
§102(a)(1): public disclosures
A person shall be entitled to a patent unless the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date.
| Category | Covers |
|---|---|
| Patented | Any country's granted patent |
| Described in a printed publication | Any publicly accessible document |
| In public use | Use accessible to the public |
| On sale | A commercial offer for sale |
| Otherwise available to the public | The catch-all |
Five categories, one test underneath them: public availability.
"Otherwise available to the public" was added by the AIA and does real work. An oral presentation, a demonstration, a poster, an electronic posting — none is a printed publication in the ordinary sense, and all can be prior art.
§102(a)(2): earlier-filed applications
...the claimed invention was described in a patent issued, or in an application published, that names another inventor and was effectively filed before the effective filing date of the claimed invention.
| Feature | Effect |
|---|---|
| Applies from | Its own effective filing date |
| Becomes prior art when | It publishes or issues |
| Must name | Another inventor |
| Practical consequence | An unpublished application can become prior art retroactively |
This is the provision that makes searching incomplete by definition. An application filed last year is invisible today and will be prior art from its filing date once it publishes.
Which is the eighteen-month blackout. No search can see it, and no tool can promise otherwise. See patent invalidity search.
§102(b): the exceptions
Two exceptions, each split into the (a)(1) and (a)(2) versions.
| Exception | Removes |
|---|---|
| 102(b)(1)(A) | A disclosure within 1 year, made by the inventor or someone who obtained it from them |
| 102(b)(1)(B) | A disclosure within 1 year, where the inventor had already publicly disclosed it |
| 102(b)(2)(A) | Earlier-filed subject matter obtained from the inventor |
| 102(b)(2)(B) | Earlier-filed subject matter already publicly disclosed by the inventor |
| 102(b)(2)(C) | Earlier-filed applications commonly owned at the time |
The grace period is personal, not general. It removes your own disclosure from the art against your own application. It does nothing about a third party's independent publication.
102(b)(1)(B) is the shield provision. Once you have publicly disclosed, a third party's subsequent disclosure of the same subject matter within your grace period does not count against you.
102(b)(2)(C) matters inside companies. Applications commonly owned at the time of filing are not prior art against each other, which prevents a company's own earlier filings blocking its later ones.
The effective filing date
| Which date | When it applies |
|---|---|
| Actual filing date | Default |
| Provisional filing date | If the provisional supports the claim |
| Foreign priority date | If properly claimed and supported |
| Parent application date | For continuations and divisionals |
| Date of invention | No longer relevant post-AIA |
Priority is only as good as the disclosure supporting it. A claim not enabled by the provisional does not get the provisional's date, which can open a window of art the applicant assumed was excluded.
Establishing the correct date is the first step in any prior art analysis, and getting it wrong invalidates everything downstream.
Reading the section in order
The structure repays reading straight through, because the exceptions only make sense against the categories they modify.
| Provision | Function |
|---|---|
| §102(a)(1) | Public disclosures before the filing date |
| §102(a)(2) | Earlier-filed applications by another |
| §102(b)(1) | Exceptions to (a)(1) |
| §102(b)(2) | Exceptions to (a)(2) |
| §102(c) | Common ownership under joint research agreements |
| §102(d) | When a patent or application is "effectively filed" |
Subsection (d) is the definitional plumbing. It establishes that an application is effectively filed as of its earliest priority date for §102(a)(2) purposes, which is what makes an unpublished application prior art retroactively.
§102(c) extends common ownership to joint research agreements. Parties to a qualifying agreement are treated as commonly owned for the exception, which is designed so that collaboration does not create prior art between collaborators.
The public accessibility test
Running through every category is one question: could an interested person exercising reasonable diligence have found it?
| Item | Prior art? |
|---|---|
| Journal article, indexed | Yes |
| Thesis catalogued and shelved | Yes |
| Conference paper in published proceedings | Yes |
| Poster displayed at a conference | Usually |
| Product manual shipped with a product | Yes |
| Internal memo, three recipients | No |
| Document under NDA | No |
| Web page, if datable | Yes |
Actual readership is irrelevant. Nobody needs to have read it.
Indexing usually decides it. A document findable through a catalogue is accessible; one with no finding aid may not be. See non-patent literature.
"On sale" after Helsinn
| Position | Detail |
|---|---|
| A commercial offer for sale | Prior art |
| Confidential sale, invention details secret | Still prior art — Helsinn v. Teva |
| Sale by the inventor | Counts, subject to the grace period |
| Supply agreement | Can qualify |
| An offer, without any sale | Can qualify |
Helsinn settled a question the AIA text had left open. A sale triggers the bar even where the invention itself was not disclosed publicly in the transaction.
Which catches companies routinely. A supply agreement or a purchase order more than a year before filing can bar the patent, and the paperwork exists in the company's own records.
Anticipation versus obviousness
Being prior art is one question; what it does is another.
| Provision | Requires |
|---|---|
| §102 anticipation | One reference disclosing every element as claimed |
| §103 obviousness | Several references, with a reason to combine |
Section 102 defines the universe of art. Section 103 then asks whether that art, combined, would have made the invention obvious to a person of ordinary skill.
A reference that is prior art but discloses only three of five elements does not anticipate. It may still contribute to an obviousness case alongside another reference.
Which is why the definition matters before the analysis. A document that is not prior art at all cannot support either ground, however damaging its content.
Pre-AIA and post-AIA
| Pre-AIA (before 16 March 2013) | Post-AIA | |
|---|---|---|
| Governing date | Date of invention | Effective filing date |
| First to | Invent | File |
| Geographic limits on some categories | Yes — public use and sale were US-only | No |
| Prior invention by another | A category | Removed |
| Interference proceedings | Available | Replaced by derivation |
| Grace period | 1 year, broader | 1 year, narrower |
Older patents are examined under the old rules. A patent with an effective filing date before 16 March 2013 follows pre-AIA §102, which is why an invalidity analysis must establish which regime applies before anything else.
The geographic change matters. Under pre-AIA law, public use and sale had to be in the US to count. Post-AIA, they count anywhere.
Common misreadings
| Belief | Correct position |
|---|---|
| "It has to be a patent" | Any public disclosure counts |
| "It has to be in English" | Any language |
| "It has to be American" | Anywhere in the world |
| "Someone must have read it" | Accessibility, not readership |
| "My own work cannot count against me" | It can, outside the grace period |
| "A confidential sale is safe" | On sale bar applies — Helsinn |
| "The invention date protects me" | Not post-AIA |
| "An unpublished application is not art" | It becomes art from its filing date |
The two that cost the most are the self-disclosure ones. An inventor's own conference talk or confidential supply agreement, more than a year before filing, bars their own patent.
The geographic and language beliefs are pre-AIA remnants, and even then applied only to some categories.
Worked example: applying the section
An inventor filed a non-provisional on 10 June 2024, claiming a provisional filed 14 August 2023.
| Item | Date | Prior art? | Basis |
|---|---|---|---|
| Competitor's journal paper | Mar 2023 | Yes | §102(a)(1) printed publication |
| Inventor's own conference talk | Nov 2022 | No | §102(b)(1)(A) — within 1 year of 14 Aug 2023 |
| Inventor's own trade show demo | Jun 2022 | Yes | Outside the 12-month grace period |
| Third-party blog post | Dec 2022, after the inventor's talk | No | §102(b)(1)(B) shield |
| Competitor's application | Filed Jan 2023, published Jul 2024 | Yes | §102(a)(2) — from its filing date |
| Inventor's supply agreement | Mar 2022 | Yes | On sale, outside grace period |
| Sister company's application | Filed Feb 2023, commonly owned | No | §102(b)(2)(C) |
What decided each one
The effective filing date is 14 August 2023, from the provisional — so the grace period runs back to 14 August 2022.
The June 2022 demo is fatal and self-inflicted. Two months outside the grace period, and it is the inventor's own disclosure.
The competitor's application counts from January 2023, not from its July 2024 publication. It was invisible during any search run before publication.
The blog post is removed by the shield provision, because the inventor had already publicly disclosed in November 2022.
Where prior art is searched
| Source | Coverage by examiners |
|---|---|
| US patents and applications | Thorough |
| Foreign patents | Moderate |
| Journal and conference literature | Weak |
| Standards documents | Weak |
| Product manuals and datasheets | Very weak |
| Theses | Very weak |
| Archived web pages | Very weak |
Everything in §102 counts equally in law and unequally in practice. Examiners search patent databases thoroughly because those databases are structured for it.
Which is why the references that defeat a patent are so often not patents. See non-patent literature.
Foreign filing has no grace period
| Jurisdiction | Grace period for the inventor's own disclosure |
|---|---|
| United States | 12 months |
| European Patent Office | None, in practice |
| China | Very limited exceptions |
| Japan | Limited, with formalities |
| Most others | None |
A disclosure that leaves US rights intact usually destroys foreign ones on the same day. This asymmetry is the single most expensive misunderstanding about the grace period.
File before disclosing. It is the only sequence that keeps every option open.
What is not prior art
| Item | Why not |
|---|---|
| A confidential document | Not available to the public |
| An abandoned, unpublished application | Never published |
| A secret process used by someone else | Not public |
| The inventor's own disclosure within the grace period | §102(b)(1)(A) |
| Commonly owned earlier applications | §102(b)(2)(C) |
| Anything after the effective filing date | Wrong side of the line |
Secret prior use by a third party is not prior art against a later applicant, though it may support prior user rights as a defence to infringement.
Using the definition in practice
| Task | What the definition governs |
|---|---|
| Patentability search | The date cutoff and what sources to cover |
| Invalidity search | The same, from the target patent's priority date |
| Disclosure duty | What must be submitted under 37 CFR 1.56 |
| Freedom to operate | Not governed — that turns on in-force claims |
| PTAB petitions | Documentary art only, within §102/§103 |
Freedom to operate is the one that is not a prior art question at all. It looks at live claims, not at what was published, and expired patents are irrelevant to it while being fully relevant as prior art. See freedom to operate.
The disclosure duty tracks the definition. Anything material that falls within §102 must be submitted during prosecution, regardless of how it was found.
The definition in practice
Three tasks depend directly on getting the definition right.
| Task | What turns on it |
|---|---|
| Setting a search date | The effective filing date, not the filing date |
| Grading a reference | Whether it predates that date at all |
| Disclosure duty | Whether a document is material under §102 |
A search run from the wrong date is worthless. A patent filed in 2019 as a continuation of a 2013 application has a 2013 cutoff, and searching from 2019 excludes six years of the relevant window.
Grading comes second. A document that is not prior art cannot anticipate or contribute to obviousness, however closely it matches. See patent invalidity search.
Prior art definition: the checklist
- Establish the effective filing date first, following the whole priority chain.
- Check which regime applies — pre-AIA for effective filing dates before 16 March 2013.
- Work through §102(a)(1)'s five categories, ending with the catch-all.
- Check §102(a)(2) for earlier-filed applications counting from their filing dates.
- Apply the §102(b) exceptions, especially the inventor's own twelve-month grace period.
- Test public accessibility, not readership. Indexing usually decides it.
- Look for on-sale activity in your own records — supply agreements and purchase orders count, even confidential ones.
- Remember language and country are irrelevant. Prior art is prior art anywhere.
- Assume foreign rights are gone if there was any public disclosure before filing.
- Accept that no search is complete. Unpublished applications become prior art retroactively from their filing dates.