"Any person" may give notice of opposition without specifying any particular interest. "Any person" is to be construed in line with Art. 58 as meaning any natural person (private individual, self-employed persons, etc.), any legal person or any body assimilated to a legal person under the law governing it. "Any person" does not include the patent proprietor (see G 9/93, reversing G 1/84).[Art. 99(1); ]

Notice of opposition may also be filed jointly by more than one of the persons mentioned above. In order to safeguard the rights of the patent proprietor and in the interests of procedural efficiency, it has to be clear throughout the procedure who belongs to the group of common opponents. If a common opponent (including the common representative) intends to withdraw from the proceedings, the EPO must be notified accordingly by the common representative or by a new common representative determined under Rule 151(1) in order for the withdrawal to take effect (see also G 3/99).

Oppositions are not assignable but may be inherited or succeeded to as part of an overall succession in law, e.g. in the event of the merger of legal persons (see G 4/88). Acquiring companies may also take over oppositions filed by acquired companies. However, a legal person who was a subsidiary of the opponent when the opposition was filed and who carries on the business to which the opposed patent relates cannot acquire the status of opponent if all its shares are assigned to another company (see G 2/04).

The European Patent Office has to examine, ex officio, the validity of any purported transfer of opponent status to a new party at all stages of the proceedings (see T 1178/04).