R. 76(1) EPC (Art. 99(1) EPC 1973) provides, inter alia, that "notice of opposition shall be filed in a written reasoned statement". R. 76(2)(c) EPC (R. 55(c) EPC 1973) requires the notice of opposition to contain, inter alia, "a statement of the extent to which the European patent is opposed" (see also in this chapter IV.C.2.2.6).

In G 9/91 (OJ 1993, 408) the Enlarged Board clarified that the power of an opposition division or a board of appeal to examine and decide on the maintenance of a European patent under Art. 101 and 102 EPC 1973 (now merged in Art. 101 EPC) depends on the extent to which the patent is opposed in the notice of opposition (R. 55(c) EPC 1973; R. 76(2)(c) EPC). However, this principle is subject to a restriction: even if the opposition is expressly directed only against the subject-matter of an independent claim in a European patent, claims which depend on any such independent claim can nonetheless also be examined as to their patentability if the independent claim is eliminated in opposition or appeal proceedings, provided that the validity of these dependent claims is put in doubt prima facie by the information which is already available (cf. also T 443/93, T 31/08; the principles set out in G 9/91 have been followed by subsequent case law, e.g. T 1019/92, T 1066/92, T 1350/09; see also T 525/96 and T 907/03 in respect of claims of an auxiliary request).

The statements in the notice of opposition relevant to the extent to which the European patent is opposed should be interpreted in such a way that an addressee would understand them, taking into account the surrounding circumstances (T 376/90, OJ 1994, 906; see also T 1/88, in which the board based its interpretation of equivocal procedural acts on the "objective value of the declaration"). In the light of G 9/91, the board in T 376/90 doubted that the general practice of interpreting the absence of such statements as an indication of the opponent's intention to oppose the patent concerned in its entirety could be continued. See however also T 764/06, in which the board concluded from the absence of a statement under R. 55(c) EPC 1973 that the patent was opposed only to a certain extent that the patent in suit was opposed in its entirety.

In T 114/95 the board held that if an opponent requested revocation of the patent in its entirety, it was sufficient to substantiate the ground(s) for opposition in respect of at least one claim of the patent for the requirements of R. 55(c) EPC 1973 (R. 76(2)(c) EPC) to be met. R. 55(c) EPC 1973 did not refer to claims but rather required that the notice of opposition should contain a statement of the extent to which the patent was opposed (see also e.g. T 938/03 and T 1900/07; see however the different opinion in T 737/92, requiring that claims are actually opposed, as distinct from being merely formally mentioned in the notice of opposition).

In T 938/03 the board highlighted that the extent to which a patent was opposed did not depend on the second requirement under R. 55(c) EPC 1973 (R. 76(2)(c) EPC), namely the indication of the grounds of opposition and the facts, evidence and arguments in support of these grounds. Rather, the extent to which a European patent is opposed was exclusively determined by what has been implicitly (see T 376/90, OJ EPO 1994, 906) or explicitly indicated (in the case at issue by ticking the relevant box in EPO form 2300).