In the first three decades of the twentieth century, two groups of radical political theorists - one British and one American - were bound together in a unique ideological relationship. Progressives, Pluralists, and the Problems of the State provides the first comprehensive examination of the intellectual dialogue that constituted that bond. Drawing on extensive original archival research, and employing new methods of conceptual analysis, the book examines the efforts of these two initially distinctive political movements to forge a single ideology capable of motivating far-reaching reform in both of their countries. In so doing it challenges traditional narratives emphasizing the exceptional development of American progressivism and British socialism, arguing instead that the intellectual inspirations and political programmes of both movements were constantly shaped and reshaped by international ideological exchange. Such an analysis transforms our understanding of the complex political demands of these movements and enables the works of their leading protagonists, including G. D. H. Cole, Herbert Croly, Harold Laski, and Walter Lippmann, to emerge as rich and sophisticated contributions to modern political thought.