Invalidity search
Also called validity search, patent validity search, invalidity prior art search, patent invalidation search
Invalidity search, also called a validity search, is a search done after a patent is granted for any publication (prior art) that can be used to prove that one or more claims of the patent are invalid1.
WIPO lists current or anticipated litigation, licensing negotiations and due diligence on the value of a patent as the reasons validity searches are done1. The documents sought are those that could challenge the patent's novelty or inventive step1.
What the search looks for
To challenge the validity of a patent, WIPO says you search for patent or other documents that could challenge its novelty or inventive step, including issued patents and other published prior art1. The same documents can render a patent partially or completely invalid1.
Most prior art must have been made public before the relevant date. In the US this is the effective filing date of the claimed invention (35 U.S.C. 102(a)(1))2. US patents, published US applications and applications deemed published under 35 U.S.C. 122(b) that were effectively filed earlier also count, even if they were published later (35 U.S.C. 102(a)(2))2. A disclosure made 1 year or less before the effective filing date by the inventor, or by another who obtained the subject matter from the inventor, is not prior art under 102(a)(1) (35 U.S.C. 102(b)(1)(A))2. The same applies where the subject matter disclosed had, before that disclosure, been publicly disclosed by the inventor, a joint inventor or someone who obtained it from them (102(b)(1)(B))2. Patents on applications filed before March 16, 2013 are judged under pre-AIA 35 U.S.C. 102 and 10311. Under the EPC the date is the date of filing (Article 54(2))3, or the priority date where priority is claimed (Article 89)4. Earlier-filed European applications published on or after that date also count, for novelty (Article 54(3))3.
- Patents and published applications. WIPO describes the aim as uncovering issued patents or other published prior art that may render a patent partially or completely invalid1.
- Documents that are not patents. WIPO describes the search as covering patent or other documents1. See non-patent literature. In a US inter partes review, however, the prior art is limited to patents or printed publications5.
- Use and other forms of public availability. The EPC state of the art covers written or oral description, use, or any other way of making something available to the public3. US law lists public use, sale and anything otherwise available to the public alongside publications2.
Where the results are used
The search itself does not change a patent. Its results are used in a procedure that can. WIPO names litigation as one setting1. The tabs below show routes for challenging a granted patent in the US, Europe and China.
United States
- In any action involving the validity or infringement of a patent, invalidity of the patent or any claim in suit on any ground specified in part II as a condition for patentability is a defense that must be pleaded (35 U.S.C. 282(b)(2))6.
- A patent is presumed valid, each claim independently of the others, and the burden of establishing invalidity rests on the party asserting it (35 U.S.C. 282(a))6.
- A third party, meaning a person who is not the owner of the patent, can ask the USPTO to review claims through inter partes review. It is limited to grounds under 35 U.S.C. 102 or 103 and to prior art consisting of patents or printed publications5. Institution is discretionary: the Director may authorize review only if there is a reasonable likelihood that the petitioner would prevail on at least 1 challenged claim, and the decision whether to institute is final and nonappealable (35 U.S.C. 314(a) and (d))19. The USPTO proposed changes to its rules for instituting inter partes review in a notice of proposed rulemaking published on 17 October 2025, and no final rule had been published in the Federal Register as of 27 October 202618.
Europe
- Within nine months of the publication of the mention of grant, any person may give notice of opposition to a European patent (Article 99(1) EPC)7.
- Opposition may only be filed on the grounds in Article 100 EPC: the subject-matter is not patentable under Articles 52 to 57, the patent does not disclose the invention sufficiently clearly and completely, or the subject-matter extends beyond the application as filed8.
- If at least one ground prejudices the maintenance of the patent, the Opposition Division revokes it; otherwise it rejects the opposition (Article 101(2))9. See opposition search.
- In national proceedings, a European patent may be revoked with effect for a contracting state only on the grounds in Article 138(1) EPC, which include the opposition grounds13. When such an action can be brought depends on national law.
- For Unitary Patents and for European patents within its jurisdiction, the Unified Patent Court offers a central revocation action, separate from EPO opposition, at any time during the life of the patent14. See Unified Patent Court.
China
- Beginning from the announcement of grant, any entity or individual that considers the grant not in conformity with the Patent Law may request the patent administration department under the State Council to declare the patent right invalid (Article 45)10.
- A party that does not accept the decision may file a lawsuit in the people's court within three months from the date of receipt of the notification (Article 46)10.
- The grounds for invalidation are limited to those listed in Rule 69(2) of the Implementing Regulations12.
What a prior art search does not cover
Prior art supports only some grounds of invalidity. The routes allow different grounds5,6,8, which decides how much of a search can be used.
| Route | When it can start | Grounds or prior art allowed |
|---|---|---|
| US court defense | In any action involving the validity or infringement of a patent6 | Any ground specified in part II as a condition for patentability, and failure to meet any requirement of section 112, except that failing to disclose the best mode is not a basis for invalidity6 |
| US inter partes review | For first-inventor-to-file patents, after the later of 9 months from grant or the end of an instituted post-grant review5; not if the petition is filed more than 1 year after the petitioner, its real party in interest or privy was served with an infringement complaint (35 U.S.C. 315(b))17. The 9-month wait does not apply to first-to-invent patents5 | Grounds under 35 U.S.C. 102 or 103 only, and only prior art consisting of patents or printed publications5 |
| EPO opposition | Within nine months of the publication of the mention of grant7 | Articles 52 to 57 (patentability), insufficient disclosure, and added subject-matter8 |
| National or UPC revocation (Europe) | UPC: at any time during the life of the patent, for patents within the UPC's jurisdiction14. National courts: as national law provides. | Article 138(1) EPC grounds, which include lack of patentability, insufficiency and added matter13 |
| China invalidation request | Beginning from the announcement of grant10 | Only the grounds listed in Rule 69(2) of the Implementing Regulations, which include novelty and inventiveness (Article 22), sufficiency and support (Article 26(3) and (4)) and added matter (Article 33)12 |
Invalidity search vs other patent searches
| Search | Question it answers | When it is done |
|---|---|---|
| Invalidity (validity) search | Was the patent properly granted?1 | After the patent is granted, for example because of litigation, licensing negotiations or due diligence1 |
| Patentability search | Is the invention new and non-obvious over the prior art?1 | While preparing and before filing a patent application1 |
| Infringement (FTO) search | Would unexpired patents be infringed by launching a product?1 | During technical development, product development or before marketing1 |
The two are linked. WIPO notes that if an infringement search uncovers a patent that poses an infringement risk, a validity search may be performed to help determine whether that patent is valid1.
Questions people ask
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Run Novelty SearchWhat is the difference between an invalidity search and a validity search?
None: they are two names for the same search. WIPO uses the term validity search for a search, done after grant, that looks for publications to prove that one or more claims are invalid1. This page uses invalidity search for the same kind of search.
When is an invalidity search done?
After a patent is granted. WIPO says such searches are done because of current or anticipated litigation, in licensing negotiations, and as part of due diligence on a patent's value1.
Can the same prior art be used in every challenge route?
No. A US inter partes review is limited to patents or printed publications5, while an EPO opposition may rely on the state of the art, which includes written or oral description and use3,8. A US court defense may rely on any ground specified in part II as a condition for patentability6.
Is a granted patent assumed to be valid?
In the US, yes. A patent and each of its claims is presumed valid, and the party asserting invalidity carries the burden of establishing it6. In court, invalidity must be proved by clear and convincing evidence15. In an inter partes review, the petitioner must prove unpatentability by a preponderance of the evidence (35 U.S.C. 316(e))16.
How it connects
Go from the term to the task
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- 01 / How-toHow to run a freedom-to-operate analysisScope, search, claim review and the report counsel will ask for.Read
- 02 / AI agentFTO Search AI AgentAn AI agent that finds in-force patents that could read on your product, with a claim chart for each one.Run it
- 03 / Free toolAI prior art searchDescribe an idea, get the closest patents.Try tool