What Is Prior Art?
Prior art is any evidence that an invention was already known, published, used or sold before a patent application's effective filing date, and it can block a patent.
How it works
When a patent examiner reviews an application, they search for prior art: earlier patents, published applications, journal articles, products, websites and other public information related to the invention. If prior art shows the invention is not new, or is an obvious variation of what was known, the examiner can reject the claims.
Prior art is not limited to patents or to the United States. A public product demonstration, a conference talk or a web post by anyone, including the inventor, can count, depending on timing and the rules in each country. The US has a limited grace period for an inventor's own disclosures, while many other countries are stricter, so timing needs care.
Example
For example, a founder invents a new way to schedule deliveries and later learns that a published academic paper describes the same method. The paper may be prior art that prevents a patent on that method. The founder could still file narrower claims, but only on aspects the paper does not disclose.
Why founders care
A prior art search before investing in a patent filing can reveal whether an idea is likely to be patentable and what the competitive field looks like. A search is imperfect, because it cannot cover everything, and results are not a guarantee either way. Founders should also avoid publishing or selling an invention before talking with a patent professional about deadlines.
Common mistakes
- Assuming no one has done it before without searching.
- Searching only patents and ignoring products and papers.
- Making a public disclosure before filing.
- Ignoring foreign deadlines when relying on a US grace period.
Frequently asked questions
What is prior art?
Prior art is any publicly available evidence that an invention, or something close to it, existed before the application's effective filing date. It includes patents, publications, products and public uses, and it can prevent a patent.
Can my own disclosure be prior art?
It can be. In the US there is a limited grace period for an inventor's own disclosures, but many other countries have no such period. Check timing with a patent professional before disclosing.
Related terms
Go deeper
- Provisional Patent Application: A Startup Guide IP guideHow a provisional patent application works for startups: the 12-month deadline, what it protects, patent pending meaning, and provisional vs nonprovisional.
- Patent Attorney vs Patent Agent for a Startup IP guidePatent attorney vs patent agent: what each can do, how costs differ, how to hire one for your startup, and how to verify a practitioner on the USPTO roster.
- Do I Need a Patent for My App? A Founder's Guide IP guideDo I need a patent for my app? Learn what software patents cover, why eligibility is a hard question, and what protects an app without one.
All 70 startup terms · More terms starting with P · Guides
General information, not legal, tax or financial advice. Reviewed 11 November 2026.