Relations with third countries are becoming more and more important for the EU, and the EU must ensure the protection of its interests in relation to developments which will have a substantial effect on it. The authors pay great attention to the association as a special partnership of EU Member States with a third country, which provides for deepened relations in political, economic, environmental and other spheres of cooperation. It is concluded that the legal nature of the Association Agreements between the EU and third countries is that they envisage deepened EU relations with third countries in different areas of cooperation and are distinguished by a significant specificity, which is manifested in the following features: the third country does not participate in the founding treaties of the EU, instead, association agreements provide for the establishment of a special institutional mechanism; the third country does not join the work of the EU institutions; instead, association agreements provide for the establishment of a special institutional mechanism; the creation of an association is based on an economic, political and legal basis. The authors carefully examine the features of associative agreements in the practice of the European Union’s external relations. The number and variety of relevant treaty norms testify to the formation of a special institute of ‘association’ in the practice of the European Union.