Prior art is, in general, all the knowledge that existed prior to the relevant filing or priority date of a patent application, whether it existed by way of written and oral disclosure.  In some legal instruments there is a differentiation between printed publications, oral disclosures and prior use and where the publications or disclosure occurred.

For the purposes of the PCT, prior art is defined by Rule 33.1 of the PCT Regulations as “everything which has been made available to the public anywhere in the world by means of written disclosure (including drawings and other illustrations) and which is capable of being of assistance in determining that the claimed invention is or is not new and that it does or does not involve an inventive step (i.e. that it is or is not obvious), provided that the making available to the public occurred prior to the international filing date.”

In Europe, Article 54(2) of the European Patent Convention (EPC) defines the equivalent term “the state of the art” as comprising “everything made available to the public by means of a written or oral description, by use, or in any other way, before the filing of the European patent application.”  With reference to this provision of the EPC, the Guidelines for Examination in the European Patent Office (EPO) emphasize that “[t]he width of this definition should be noted.  There are no restrictions whatever as to the geographical location where, or the language or manner in which the relevant information was made available to the public; also no age limit is stipulated for the documents or other sources of the information.  However certain specific exclusions exist (see IV, 8).”

Section 35 of the United States Code 102 defines prior art indirectly through the concept of novelty as anything ”known or used by others in this country, or patented or described in a printed publication in this or a foreign country, before the invention thereof by the applicant for patent …”.

Section 29 of Japanese Patent Law indirectly defines “prior art” as  “(i) inventions that were publicly known in Japan or a foreign country, prior to the filing of the patent application;
(ii) inventions that were publicly worked in Japan or a foreign country, prior to the filing of the patent application; or  (iii) inventions that were described in a distributed publication, or inventions that were made publicly available through an electric telecommunication line in Japan or a foreign country, prior to the filing of the patent application.”