Guide for applicants, Part 2: PCT procedure before the EPO (Euro-PCT Guide)

Any attorney, patent agent or other person ("agent") having the right to practise before the national or regional patent office with which the international application was filed is entitled to practise before: 

Two or more applicants may choose to appoint either a common agent for the international phase or one of the said applicants who is a national or resident of a PCT contracting state to act as their common representative, who in turn may then appoint an agent.

If no common agent or common representative has been appointed, the applicant first named in the request who is entitled to file an international application with the EPO as receiving Office is considered to be the common representative (see points 100 ff). The "deemed common representative" is not entitled to sign notices of withdrawal on behalf of co-applicants. If a deemed common representative has appointed an agent, the latter may validly perform any act which could be performed by the deemed common representative.