As the author of the ground-breaking work of Marxist political economy, Finance Capital, and a leader in the German Social Democratic Party, Rudolf Hilferding was a dominant intellectual and political figure in the history of European socialism from its halcyon days in the pre-1914 era until its collapse in the 1930s. This collection of his previously unpublished correspondence allows readers to trace the evolution of Hilferding’s thought as socialism’s fortunes declined and his own fate became precarious. It shows how, in the face of rising Stalinism and fascism, democracy remained at the core of his socialist vision.