Bulgarian Georgi Dimitrov, Stalin's close confidant and trusted ally, served as secretary general of the Communist International (Comintern) from 1934 to its dissolution in 1943. In this revealing collection of more than fifty top-secret letters, the real workings of the Comintern emerge clearly for the first time. Drawn from classified Soviet archives only recently opened to Russian and American scholars, these letters offer unique insights into Soviet foreign policy and Stalin's attitudes and intentions while the Great Terror of the 1930s was in progress and in the years leading up to the Second World War. Annotated by the editors to provide the historical context in which these letters were written, the collection is vivid and startlingly significant. The letters confirm the complete dependence of the Comintern on the Kremlin, while also exposing bureaucratic manoeuvering, backbiting, and jockeying for influence. These messages cast much new light on the Soviet confusion about policies toward foreign Communist parties, and they uncover the extent to which Stalin shaped the Comintern. Stalin's perspectives on America, French communism, and the Spanish Civil War are recorded, as are his differences with Mao Zedong and with Marshal Tito at important turning points. With the publication of these letters, the history of twentieth-century communism gains authentic new evidence about a critical decade.