The Three Seas Initiative (3SI), also known as the Baltic, Adriatic, Black Sea Initiative, is a regional forum that unites thirteen European Union states along a north-south axis from the Baltic to the Adriatic and Black Seas. Launched in 2015 by Polish President Andrzej Duda and Croatian President Kolinda Grabar-Kitarović, the initiative seeks to strengthen economic cooperation, accelerate infrastructure development, and bolster energy security among Central and Eastern European nations.