Central Europe is a recurring theme in Polish foreign and security policy. Its newest manifestation is the Three Seas Initiative (3SI, Trimarium), which Poland has been pushing for since 2015. This initiative harks back to earlier attempts to organize cooperation under Poland’s leadership between Central and Eastern European countries and is an expression of Poland’s desire to attain the great power position it once held in distant history. The 3SI is limited to close cooperation between twelve countries lying on the eastern fringes of the EU and NATO but does not involve Ukraine or Belarus, which are traditionally included in Poland’s initiatives. The author discusses the essence of the 3SI, its potential, and the obstacles involved in its implementation.