Prior art or state of the art is all information that has been disclosed to the public in any form before a given date. Prior art does not include information kept secret, whether from trade secrecy or just a simple lack of interest in publication. Normally, we expect prior art to be descriptions sufficient to inform the average worker in the field (or the man skilled in the art), published in fixed form and made available in public libraries. Normally, prior art does not include unpublished work or mere conversations (though according to the European Patent Convention, oral disclosures also form prior art - see Art. 54(2) EPC.
The term prior art is mainly used in the patent field. Patents disclose to society how an invention is practiced, in return 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 and all first-to-invent patent systems) or before the filing date (in Europe and all first-to-file patent systems).
First-to-invent systems
The invention date can be legally bounded by descriptive documents signed by witnesses who understand the invention and can testify about what the inventor knew as of that date. The latest possible bound for the invention date is the patent application date. The United States uses a first-to-invent system.
First-to-file systems
Most countries other than the United States use a First-to-file system. This means that, regardless of who the first inventor was, the person who files a patent application first is the one who is granted the patent rights on the invention. The First-to-invent versus First-to-file rule is one of the major dichotomies between U.S. patent law and the patent laws of many other nations. As of this writing (2004), harmonization efforts are underway with the goal being to unify the patent laws of various nations so that inventors have the same rights regardless of in which country a patent is granted.
Other considerations
While patents normally go to the first inventor, an inventor who keeps the information secret or just does not publish generally loses the right to the patent and also does not establish prior art. Without prior art, a later inventor can get a valid patent on the same invention and then apply it against earlier inventor(s). All this is easily prevented simply by recognizing the invention and applying for a patent, or by publishing details of how to practice the invention, thus creating prior art.
Prior art searching
Prior art searches are often conducted before filing a patent application. A prior art search helps an inventor determine if the invention is novel before committing the resources necessary to obtain a patent. This type of search is called a novelty search. Prior art searches may also be used to invalidate existing patents (these searches are called "validity searches" or "invalidity searches") by showing that the patent office erred in the issuance of a patent because the patent holder is not the first inventor. Prior art searches are also useful to determine what a patent or patent application is really worth, before acquiring it or taking a license.
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