INTRODUCTION. The article is devoted to the process of accession of new states to the European Union (EU). The authors try to demonstrate the evolution of the procedure for admitting new members since the formation of the European Communities and identify the main subjects of this procedure.MATERIALS AND METHODS. The current research is based on various international legal documents, including the founding treaties of the European Union, as well as acts of EU institutions and doctrinal sources.RESEARCH RESULTS. The research represents a retrospective analysis of the formation of the procedure for accession of new members to the European Communities/EU. It was found out that the norms of the founding agreement set only the general legal framework of the procedure, and its specific content differed through out the existence of the European integration project. The actual content of the accession process is determined by the member states, which, through the institutions of the Communities/Union, primarily the Council and the European Council, formulate the criteria and principles of accession. The Commission also plays a significant role in the process. The role of the European Parliament in this procedure is insignificant, although this institution tries to increase its influence throughout the negotiation process. DISCUSSION AND COCLUSION. To sum up, the accession procedure is typologically close to a special legislative procedure. Since its origin the accession of new states to the EU has been transformed from a rule-making procedure enshrined in the founding treaties to a set of various instruments and practices, including non-legal (political) ones.