This book begins a series of publications devoted to political reflection on the integration of Central and Eastern Europe with the participation, or even under the aegis, of Poland. The attempts to make it happen have lasted from the late nineteenth to the outset of the twenty-first century. The idea of organized order in the central and eastern part of the continent that aimed to ensure the security of Poland and stability of the region, took various forms: from Piłsudski's federation concept through the Intermarium and the idea of Giedroyc’s ULB to the Three Seas Initiative promoted by Poland in recent years. The vitality and diversity of this idea is undoubtedly a historical phenomenon, which has become the subject of analyses of well-known Polish historians and political scientists in this volume.