Opposition proceedings are contradictory inter partes proceedings between one or more opponents and the patent proprietor, similar to regular court proceedings. They are governed by the European Patent Convention (EPC), by the Implementing Regulations and by the Guidelines (Part D). In addition, the appeal procedure before the Technical Boards of Appeal follows the Rules of Procedure of the Boards of Appeal. The Boards of Appeal are not bound to apply the Guidelines.
In opposition proceedings each party may use any of the three official languages of the European Patent Office, namely English, German or French. Oral proceedings are held in the language of the proceedings, which is the language in which the application resulting in the opposed patent was published by the EPO. Nevertheless, each party may express itself in any of the three official languages. To this end, interpretation between the three official languages is provided, at no extra cost for the parties, on prior request of any party. Communications from the Opposition Divisions and their final decisions are, however, always issued in the language of the proceedings.
The Opposition Divisions and Technical Boards of Appeal of the European Patent Office decide opposition cases based on their own technical expertise. While the law allows the appointment of an expert, if required, the taking of evidence by appointing a technical expert is actually rarely ordered ex officio. However, the parties may present their own private experts, who may submit their opinions in writing and also, upon prior notice to the EPO, at oral proceedings.
In European opposition proceedings, a party may be represented by a professional representative admitted to practice before the European Patent Office, in particular by a European Patent Attorney.
A very important aspect of opposition proceed- ings is that, although the opponent may withdraw the opposition at any time, such withdrawal does not necessarily terminate the opposition proceedings. The Opposition Division may continue the proceedings on its own motion and issue a decision within the framework of the original opposition. This particularity of European opposition proceedings must be taken into account in settlement considerations between opponent and patent proprietor, since an opposed patent may still be revoked although the opponent has withdrawn their opposition and no longer participates in the proceedings. The withdrawal of the (only) appeal will, however, terminate the second instance opposition appeal proceedings.