Prior art

Prior art (state of the art or background art), in most systems of patent law, is constituted by all information that has been made available to the public in any form before a given date that might be relevant to a patent's claims of originality. If an invention has been described in the prior art or would have been obvious from what has been described in the prior art, a patent on that invention is not valid.
Information kept secret, for instance, as a trade secret, is not usually prior art, provided that employees and others with access to the information are under a non-disclosure obligation. With such an obligation, the information is typically not regarded as prior art. Therefore, a patent may be granted on an invention, even though someone else already knew of the invention. A person who used an invention in secret may in some jurisdictions be able to claim "prior user rights" and thereby gain the right to continue using the invention. As a special exception, earlier-filed and unpublished patent applications do qualify as prior art as of their filing date in certain circumstances.
To anticipate the subject-matter of a patent claim, prior art is generally expected to provide a description sufficient to inform an average worker in the field (or the "person skilled in the art") of some subject matter falling within the scope of the claim. Prior art must be available in some way to the public, and in many countries, the information needs to be recorded in a fixed form somehow. Prior art generally does not include unpublished work or mere conversations (though according to the European Patent Convention, oral disclosures also form prior art—see ). It is disputed whether traditional knowledge ("e.g.," of medical properties of a certain plant) constitutes prior art.
Patents disclose to society how an invention is practiced, in return for the right (during a limited term) to exclude others from manufacturing, selling, offering for sale or using the patented invention without the patentee's permission. Patent offices deal with prior art searches in the context of the patent granting procedure.
Effective date of patents and patent applications as prior art.
It is typical for a patent office to treat its own patents and published patent applications as prior art as of their filing dates, although under the European Patent Convention, this applies only to novelty rather than inventive step. However, United States patent law before the Leahy-Smith America Invents Act (AIA) included the Hilmer doctrine, under which United States patents and patent application publications were prior art only as of their earliest effective United States filing dates, i.e., disregarding any foreign priority claimed in those patents and patent application publications. The AIA has abolished the Hilmer doctrine and makes United States patents and patent application publications that name another inventor prior art as of when they were "effectively filed."
Usage in litigation.
Arguments claiming prior art are used in defending and attacking patent validity. In one U.S. case on the issue, the court said:
Types of prior art searches.
Novelty.
A "novelty search" is a prior art search that is often conducted by patent attorneys, patent agents or professional patent searchers before an inventor files a patent application. A novelty search helps an inventor to determine if the invention is novel before the inventor commits the resources necessary to obtain a patent. The search may include searching in databases of patents, patent applications and other documents such as utility models and in the scientific literature. Novelty searches can also be used to help an inventor determine what is unique about their invention. Anything not found in the prior art can be potentially patentable. Thomas Edison, for example, did not get a patent on the basic concept of the light bulb. It was already patented and therefore in the prior art. Instead, Edison got a patent on his improvements to the light bulb. These improvements included a very thin filament and a reliable technique for joining the white hot filament to the room temperature lead wires.
A novelty search is also conducted by patent examiners during prosecution of the patent application. For instance, examiner's search guidelines applicable to the United States are found in the U.S. Manual of Patent Examining Procedure (MPEP) 904.02 General Search Guidelines, Prior Art, Classification, and Search.
Validity.
A "validity search" is a prior art search done after a patent issues. The purpose of a validity (or invalidity) search is to find prior art that the patent examiner overlooked so that a patent can be declared invalid. This might be done by an entity infringing, or potentially infringing, the patent, or it might be done by a patent owner or other entity that has a financial stake in a patent to confirm the validity of a patent. Crowdsourcing, where a large number of interested people search for prior art, may be effective where references would otherwise be difficult to find.
Clearance.
A clearance search is a search of issued patents to see if a given product or process violates someone else's existing patent. If so, then a validity search may be done to try to find prior art that would invalidate the patent. A clearance search is a search targeting patents being in force and may be limited to a particular country and group of countries, or a specific market.
Duty of disclosure.
In the United States, inventors and their patent agents or attorneys are required by law to submit any references they are aware of to the United States Patent and Trademark Office that may be material to the patentability of the claims in a patent application they have filed. The patent examiner will then determine if the references qualify as "prior art" and may then take them into account when examining the patent application. If a person having a duty to disclose, acting with deceptive intent, fails to properly disclose the material references of which they are aware, then a patent can be found unenforceable for inequitable conduct.
Japan also has a duty of disclosure.
Australia has abolished its duty of disclosure with regard to the results of documentary searches by, or on behalf of, foreign patent offices, except where: 
Public participation in patent examination.
With the advent of the Internet, a number of initiatives have been undertaken to create a forum where the public at large can participate in prior art searches. These forums have been related to both issued patents and pending patent applications.
Pending patent applications.
More recently, different attempts to employ open Internet-based discussions for encouraging public participation commenting on pending U.S. applications have been started. These may take the form of a wiki:
Patent examiners often use the online encyclopedia Wikipedia as a reference to get an overall feel for a given subject. Citations of Wikipedia as actual prior art can be problematic, however, due to the fluid and open nature of its editing, and Patents Commissioner Doll said the agency used Wikipedia entries as background and not as a basis for accepting or rejecting an application.
See also.
Notable prior art databases.
For other patent search services, see "".