Joint applicants, joint proprietors of patents and more than one person giving joint notice of opposition or intervention may act through a common representative. If the request for the grant of a European patent, the notice of opposition or the request for intervention does not name a common representative, the party first named in the relevant document will be considered to be the common representative. The common representative can thus be a legal person. However, if one of the parties is obliged to appoint a professional representative and has done so, this representative will be considered to be the common representative acting on behalf of all parties. In such a case, no other party can act as common representative. However, if the first named party in the document has appointed a professional representative, that representative will be considered to be acting on behalf of all parties. If the European patent application or patent is transferred to more than one person, and such persons have not appointed a common representative, the preceding provisions will apply. If such application is not possible, the EPO will require the parties to appoint a common representative within a two-month period specified by the EPO (see E‑VIII, 1.6). If this request is not complied with, the EPO will appoint the common representative.[Art. 133(4); Rule 151(1); (2); ]

For Rule 151 to apply, each party or their duly authorised representative must have signed the document (request for grant, notice of opposition, etc.) giving rise to their participation (see also A‑III, 4.2.2 and A‑VIII, 3.2 and A-VIII, 3.4). Otherwise the party cannot take part in the proceedings, nor therefore be represented by a common representative.