The state of the art is held to comprise everything made available to the public by means of a written or oral description, by use, or in any other way, before the date of filing of the European patent application (Art. 54(2) EPC). Use can take the form of producing, offering or marketing or otherwise exploiting a product, offering or marketing a process or its application or applying the process. Marketing may be effected, for example, by sale or exchange (see Guidelines G‑IV, 7.1 – November 2018 version).

Instances of public prior use or availability in any other way will typically be raised in opposition proceedings. Under established case law (see e.g. T 194/86; T 232/89; T 78/90; T 600/90; T 602/91; T 522/94, OJ 1998, 421; T 927/98; T 805/05), the following has to be clarified to determine whether an invention has been made available to the public by prior use: (i) when the prior use occurred, (ii) what was made available to the public through that use and (iii) the circumstances of the use, i.e. where, how and by whom the subject-matter was made public through that use.

See also: chapters IV.C.2.2.8 d) "Alleged public prior use"; V.A.4.13.6 "Public prior use"; and various sections in chapter III.G. "Law of evidence".

Although prior use is dealt with here in this chapter on novelty, specifically in its section on determining the prior art, it should be borne in mind that, whilst chiefly important in that context, what can be regarded as prior art is also relevant in examining inventive step (for relatively recent examples, see e.g. T 1464/05 – public prior use as closest state of the art; T 23/11; T 2170/12).

Concerning examination by the EPO of its own motion it may be noted that under Art. 114 EPC the EPO has a limited obligation to undertake an examination of its own motion with regard to public prior use. Indeed, in T 129/88 (OJ 1993, 598) the board noted that although a board of appeal had an obligation under Art. 114(1) EPC to investigate matters of its own motion, that obligation did not extend as far as investigating an allegation of public prior use, where the party previously making that allegation had withdrawn from proceedings and it was difficult to establish all the relevant facts without that party's co-operation. The reason for this was that the obligation to investigate of its own motion imposed on the EPO by Art. 114(1) EPC was not unlimited in its scope, but was confined by considerations of reasonableness and expediency. Therefore, if the opponents withdrew the opposition, thereby indicating that they were no longer interested in the outcome of the opposition, then, although the EPO might have the power, depending on the state of residence of relevant witnesses, to compel them to give evidence, either before the EPO or before the court of a contracting state, in the interests of procedural economy it should not normally investigate the issue any further. It would be different if a relevant public prior use had already been substantiated by documents of undisputed authenticity, or if the material facts with respect to the alleged public prior use were undisputed (see T 830/90, OJ 1994, 713; T 887/90, T 634/91, T 252/93 and T 34/94).