An Extension Agreement is based on the Patent Cooperation Agreement between the European Patent Organisation on the one hand and the extension states on the other hand. It is an international treaty of the kind which the President of the EPO is authorised by the Administrative Council to conclude with the Council's approval (Art. 33(4) EPC) in order to carry out the functions assigned to him under the EPC. This agreement served the interests not only of applicants, providing as it did a simple route to patent protection in the extension states, but also those of the extension states, enabling it to offer patent protection for its territory simply by extending the effects of European and Euro-PCT applications and patents (J 14/00, OJ 2002, 432).
The boards of appeal have stated that the extension system largely corresponds to the EPC system operating in the EPC contracting states, except that it is not based on direct application of the EPC but on national law modelled on the EPC. The national law of the extension state governs the extension proceedings and the legal effects of the extension (see T 7/07).