This chapter examines the parliamentarization of the Organization for Security and Co-operation in Europe (OSCE). The establishment of the OSCE Parliamentary Assembly took place in the context of the post-Cold War democratization wave in Eastern Europe and the active diffusion efforts of the Council of Europe. Whereas the Western governments had a vested interest in ensuring the democratic transition of Eastern Europe, the young democracies sought international recognition as part of the European political community. Beyond this post-Cold War consensus, several options were under consideration. The chapter describes how the initial proposal of a joint parliamentary assembly of the OSCE with the Parliamentary Assembly of the Council of Europe (PACE) was discarded in favour of a separate OSCE Parliamentary Assembly.