Prior art

Overview
Prior art in patent law constitutes all information that was 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 prior art, a patent on that invention is not valid.

In most patent systems, in order to anticipate a claim, prior art must provide a description sufficient to inform the average worker in the field (or the person of average skill 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 many countries require the information to be recorded in a fixed form.

Patents disclose to society how an invention is practiced, in return for the right (for 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. To assess the validity of a patent application, patent offices explore the prior art that was disclosed before the invention occurred (in the United States) or before the filing date (in the rest of the world).

Trade Secrets
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. Absent such an obligation, the information will typically be regarded as prior art. Generally, this means that a patent may be granted on an invention despite the fact that someone else 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 As a special exception, earlier-filed and unpublished patent applications do qualify as prior art as of their filing date in certain circumstances.