The Three Seas Initiative, known also as the Baltic, Adriatic, Black Sea (BABS) Initiative or simply as the Three Seas, is a forum of thirteen states, in the European Union, running along a north–south axis from the Baltic Sea to the Adriatic and Black Seas in Central and Eastern Europe. The Initiative aims to create a regional dialogue on questions affecting the member states.

Intermarium was a post-World War I geopolitical plan conceived by Józef Piłsudski to unite former Polish–Lithuanian Commonwealth lands within a single polity. The plan went through several iterations, some of which anticipated the inclusion of neighbouring states. The proposed multinational polity would have incorporated territories lying between the Baltic, Black, and Adriatic Seas, hence the name Intermarium.