What Counts as Prior Art?

Written from 35 U.S.C. 102 and MPEP 2128 and 2152. The statute is law; the MPEP is examination guidance and binds no court. Current as of 22 August 2026.

The short version

Two questions, not one. Was this available to the public before your effective filing date? And separately, does an earlier-filed patent document naming another inventor reach it? The first lane is broad. The second can reach back to a filing date nobody could see.

There is a one-year grace period, and it is narrower than almost everyone expects. The page below says exactly how narrow.

Section 102 is written as an entitlement subject to exceptions rather than as a list of requirements. Its operative words are "A person shall be entitled to a patent unless" one of two conditions is met.

There are two conditions, and they work differently. Most explanations cover only the first.

Subsection (a)(1) is the public one. A patent, a printed publication, a public use, a sale, or anything otherwise available to the public before the effective filing date. That catch-all is never defined in the statute, and the Office reads it to cover a student thesis in a university library, a poster at a scientific meeting, a document posted on the internet, and more. The provision exists so the question is availability rather than whether a disclosure was technically a printed publication.

Subsection (a)(2) is not about the public at all. It reaches a claimed invention described in a patent issued under section 151, or in an application published or deemed published under section 122(b), where that document names another inventor and was effectively filed before your effective filing date.

That second lane is the one people do not see coming. An application sits unpublished for eighteen months. Under (a)(2) it can be prior art from when it was effectively filed, not from when anyone could read it. So a document nobody could have found on the day you filed may still be prior art against you. Separate exceptions in (b)(2) apply to this lane, including for subject matter obtained from the inventor and for commonly owned work.
The grace period runs back to you, not forward against the world. Both routes into the one-year exception require a chain to the inventor: either the disclosure was made by an inventor or someone who got the subject matter from them, or the subject matter had already been publicly disclosed by an inventor. An independent third party's disclosure is excepted by neither. The statute grants no grace period against someone who arrived at the same thing on their own.

The Two Bars and Their Exceptions

Section 102's two prior-art conditions and the exceptions the statute attaches to each. Every date in the section runs to the effective filing date. As of 22 August 2026.
Bar What counts as prior art Exceptions the statute gives
(a)(1), public availability 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 of the claimed invention" (b)(1): a disclosure "made 1 year or less before the effective filing date" is not prior art if it was made by an inventor or someone who obtained it from one, (b)(1)(A), or if the inventor had publicly disclosed the same subject matter first, (b)(1)(B)
(a)(2), earlier filing The claimed invention "was described in a patent issued under section 151, or in an application for patent published or deemed published under section 122(b)", naming another inventor and "effectively filed before the effective filing date of the claimed invention" (b)(2)(A) and (B) parallel the (b)(1) routes; (b)(2)(C) removes a disclosure where the subject matter and the claimed invention "were owned by the same person or subject to an obligation of assignment to the same person" by the effective filing date, and (c) deems that so for work under a joint research agreement

What the table cannot show is what the section never defines. The operative text does not say what a printed publication, a public use, a sale, or something otherwise available to the public is; those terms are left to case law and examination guidance, and the pages below take them one at a time. The word novelty appears only in the subsection heading. It is the name of the test, not a term the statute applies.

The Pages

Printed publication The test has almost nothing to do with printing. A forum post qualified because it was directed to skilled readers and sufficiently disseminated. Read the Page Available to the public The broadest phrase in the novelty statute, and the statute never defines it. On sale is the exception to it, not an example of it. Read the Page The one-year grace period Narrower than its reputation. It is tolerance for your own disclosure, not protection against someone who got there independently. Read the Page Whose provisional counts The mirror of the provisional pages. When a reference reaches back to its own provisional for an earlier prior-art date, it must show written description support for one of its published claims. Read the Case

What These Pages Do Not Decide

Nothing here tells you whether a particular act started a clock. A repository push, a demo, a conference talk, a price quote: whether any of those made an invention available to the public is a legal determination on specific facts, and it is the exact question this audience arrives with. A page cannot answer it, and one that appeared to would be the most harmful thing on this site.
  • They do not say whether your invention is novel.
  • These pages describe the America Invents Act regime. Applications filed before 16 March 2013 can be governed by different pre-AIA rules.
  • They do not say whether anything you published is prior art against you, or against anyone else.
  • They do not treat the grace period as protection or as a reason to wait. It is an exception with two narrow routes, both of which run back to an inventor.

Educational, not legal advice. If timing matters to something you are working on, that is a conversation to have with a registered patent practitioner early, because the options here close rather than open.

Related

Is it obvious? Section 102 asks whether your invention is already there. Section 103 asks the harder question: even if it is not, would getting there have been obvious? Read the Cluster Building in Public and Patents The modern way to build software is, by default, the fastest way to disclose an invention before anyone files on it. How a public commit, Show HN post, or open-source release starts the section 102 clock, why the US grace period is a fallback rather than a plan, and why foreign rights close immediately. Read the Guide When Must I File? The deadline arrives inside an ordinary commercial decision, before most companies think patents are relevant. Read the Cluster Whose provisional counts The mirror of the provisional pages. When a reference reaches back to its own provisional for an earlier prior-art date, it must show written description support for one of its published claims. Read the Case