What is Prior Art?
What counts as prior art under 35 U.S.C. § 102, the exceptions that save an applicant, and how prior art is used in examination, challenges, and litigation.
Definition
Prior art is everything made available to the public anywhere in the world before the effective filing date of a patent application, including patents, published applications, papers, products on sale, public uses, and websites, plus earlier-filed US or PCT applications by others that designate the US and publish later. An invention is patentable only if it is novel and non-obvious over the prior art.
Key Facts
- Statute: 35 U.S.C. § 102 defines what counts; § 103 governs obviousness over it
- Cutoff date: The effective filing date of the claim, including any valid priority or provisional date
- Geography: Worldwide since the America Invents Act took effect on March 16, 2013; a public use in another country now counts
- Grace period: An inventor's own disclosure within one year before filing is not prior art against them in the US, under § 102(b)(1)
- Secret prior art: An earlier-filed US or PCT application counts as prior art from its filing date even though it publishes later, under § 102(a)(2)
- Trade secrets and private uses: Not prior art, because they are not available to the public
What Qualifies
- Patents and published applications from any patent office, effective as of their filing date for § 102(a)(2) purposes and publication date otherwise
- Printed publications: Journal articles, conference papers, theses on a library shelf, standards documents, product manuals, and datasheets
- Public use: Any use of the invention accessible to the public, including a demonstration at a trade show
- On sale: An offer for sale or sale of the invention, even one where the purchaser must keep it confidential, as the Supreme Court held in Helsinn v. Teva in 2019
- Otherwise available to the public: Websites, videos, and presentations, provided the date can be proven
The Grace Period and Its Limits
US law forgives an inventor's own disclosure made within one year before filing, and also disclosures by others who obtained the subject matter from the inventor. Nearly every other jurisdiction applies absolute novelty, so the same conference talk that is harmless in the US destroys European and Chinese rights. The practical rule for IP teams is to file, at least a provisional, before any disclosure.
How Prior Art Is Used
- Examination: The examiner searches and cites references in each office action; the applicant discloses known art through an information disclosure statement
- Patentability assessment: Counsel searches before filing to draft claims that avoid the art, or to advise against filing
- Validity challenges: Inter partes review and litigation defendants search for art the examiner missed
- Freedom to operate: Prior art can invalidate a blocking patent or show a design is old and therefore free to use
Why Search Is Hard
Inventors describe the same idea in different words, the most damaging reference may be a product manual rather than a patent, and much of the relevant literature is in Japanese, Korean, or Chinese. Semantic prior art search that matches concepts rather than keywords finds references that Boolean queries miss, which is why most teams now run both.
Frequently Asked Questions
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What counts as prior art?
Any patent, published application, printed publication, public use, sale, or other public disclosure anywhere in the world before the effective filing date of the claim. Under US law an earlier-filed but later-published US or PCT application also counts from its filing date.
Does my own publication count as prior art against my patent?
In the US, not if you file within one year of the publication; the grace period in 35 U.S.C. § 102(b)(1) excludes it. In most other countries there is no grace period, so your own disclosure before filing destroys novelty.
Can prior art from another country invalidate a US patent?
Yes. Since the America Invents Act, prior art is worldwide. A public use, sale, or publication in any country before the effective filing date can anticipate or render obvious a US claim.
Is a confidential sale prior art?
Yes, in the US. The Supreme Court held in Helsinn v. Teva (2019) that a commercial sale of the invention places it "on sale" under § 102 even if the purchaser is required to keep the invention confidential.
What is the difference between prior art and the state of the art?
They are largely synonymous. "State of the art" is the term used in the European Patent Convention (Article 54), while US practice says "prior art." Both mean everything made available to the public before the relevant date.
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