As a general rule, the Opposition Division will confine its examination to those grounds for opposition brought forward by the opponent. If, for example, the opposition is filed only on the grounds that the subject-matter of the European patent is not adequately disclosed or that it extends beyond the content of the patent application as filed, the Opposition Division will examine the patentability of the subject-matter of the European patent pursuant to Art. 52 to 57 only if facts have come to its notice which, prima facie, wholly or partially prejudice the maintenance of the patent (see G 10/91, OJ 7/1993, 420).

If, therefore, once the proceedings for examining the opposition(s) have been initiated, because an admissible opposition has been filed (although it may have been withdrawn in the interim), there is reason to believe that other grounds exist which, prima facie, in whole or in part prejudice the maintenance of the European patent, these grounds should generally be examined by the Opposition Division of its own motion pursuant to Art. 114(1). Such other grounds may result from facts emerging from the search report or the examination procedure, the examiner's personal knowledge or observations presented by third parties pursuant to Art. 115 (see also E-VI, 3). Such grounds may also have been put forward in an opposition which has been withdrawn, in another opposition which has been rejected as inadmissible, or in another opposition deemed not to have been filed. They may also be any grounds submitted belatedly (see E-VI, 1.1 and 2). In carrying out such examination the Opposition Division should, however, take the interests of procedural expediency into account (see E-VI, 1.2). If the decision is to be based on grounds to be taken into account pursuant to Art. 114(1), the parties must be given the opportunity to comment (see E-X, 1).

Pursuant to Art. 100, the absence of unity of invention is not a ground for opposition (see III, 5).

Since unity of invention under Art. 82 is only required for the European patent application, the unity of the subject-matter of the European patent may not be examined by the Opposition Division, even of its own motion. In particular, where the facts, evidence and arguments which come to light in the opposition proceedings lead to the maintenance of the European patent in amended form, there should be no further examination as to whether the remaining subject-matter of the patent contains a single invention or more than one. Any lack of unity must be accepted (see G 1/91, OJ 6/1992, 253).

The grounds for opposition laid down in Art. 100 are examined in greater detail below.