The patent proprietor, the opponent(s) and, where applicable, the intervener(s) will be parties to the opposition proceedings. However, opponents who have withdrawn their opposition or whose opposition has been rejected as inadmissible will remain a party to the proceedings only until the date of such withdrawal or the date on which the decision on rejection has become final. The same will apply in the case of interveners. Third parties who have presented observations concerning the patentability of the invention in respect of which an application has been filed are not parties to opposition proceedings (see E‑VI, 3).[Art. 99(3); Art. 105(2); Art. 115; ]

Where the patent proprietors are not the same in respect of different designated contracting states, they are to be regarded as joint patent proprietors for the purposes of opposition proceedings (see D‑VII, 3.1, concerning the unity of the European patent).[Art. 118; ]

Where evidence has been provided that in a contracting state, following a final decision, a person has been entered in the patent register of that state instead of the previous patent proprietor, this person is entitled on request to replace the previous patent proprietor in respect of that state. In this event, by derogation from Art. 118, the previous patent proprietor and the person making the request are not deemed to be joint patent proprietors unless both so request. The aim of this provision is to afford new patent proprietors the opportunity of defending themselves against the opposition as they see fit (see D‑VII, 3.2, as regards the conduct of the opposition proceedings in such cases).[Art. 99(4); Art. 61(1)(a); ]

The Legal Division is responsible for decisions in respect of entries in the Register of European Patents (see the Decision of the President of the EPO dated 21 November 2013, OJ EPO 2013, 600).[Art. 20(1); ]

It is to be noted that a person who files two different notices of opposition to the same granted patent acquires party status as opponent only once (T 9/00). Two filings by the same opponent within the opposition period that individually are not admissible but taken together comply with Art. 99(1) and Rule 76 are considered as one admissible opposition (T 774/05; for a joint opposition, see D‑I, 4).

Multiple oppositions are dealt with in a single set of proceedings (see E‑III, 6). When there are multiple opponents and/or proprietors as parties to a single opposition proceedings, it is normally appropriate to deal with all relevant issues (including e.g. admissibility of one of the oppositions, see D‑IV, 5.5) when taking the final decision, e.g. during one oral proceedings (also see E‑III, 6). The legal framework is defined by the sum of the statements of the extent to which the patent is opposed and by the grounds for opposition submitted and substantiated in the notices of opposition provided by each opponent. If one of the oppositions is admissible, but is later withdrawn, prejudicial grounds put forward in said opposition are generally examined by the opposition division of its own motion. If one of the oppositions is inadmissible, and provided at least one admissible opposition has been filed, the opposition division will consider of its own motion any prima facie relevant art cited in the inadmissible opposition (see D‑V, 2.2).