Why did proposals for a federalised (Central) Europe emerge among Slovakia-related political thinkers in the mid-twentieth century, and why did they remain unrealised? Drawing on archival and library research and a contextualist approach to political thought, this monograph reconstructs Slovak federalist ideas of the 1940s and 1950s. It examines intellectuals, politicians, publicists, and diplomats with diverse backgrounds, including émigrés who explored federation as a means of securing Slovakia’s future and advancing European cooperation. For some, these proposals also offered a response to totalitarianism and communist rule. By placing these neglected projects in their Central European context, this book broadens the history of European integration beyond familiar Western European narratives and assesses competing visions of federal authority, membership, social cohesion, economic cooperation, and defence.