This study sheds new light on the Brazilian communist movement and how the specter of the USSR influenced mid-twentieth century Brazilian foreign policy. Between 1918 and 1961, Brazil and the USSR maintained formal diplomatic ties for only thirty-one months, at the end of World War II. Yet, despite the official distance, the USSR is the only external actor whose behavior, real or imagined, influenced the structure of the Brazilian state in the twentieth century. In Brazil and the Soviet Challenge, 1917–1947, Stanley Hilton examines Brazilian policy toward the Soviet Union during this period. Drawing on American, British, and German diplomatic archives and unprecedented access to official and private Brazilian records, Hilton elucidates the connection between the Brazilian elite’s perception of a communist threat and the creation of the authoritarian Estado Novo (1937–1945), the forerunner of the post-1964 national security state. Hilton shows how the 1935 communist revolt generated irresistible pressure for an authoritarian government to contain the Soviet threat; details the Brazilian government’s secret cooperation with the Gestapo during the 1930s and its concomitant efforts to forge an anti-Soviet front in the Southern Cone; and uncovers Brazil’s attempt to build counterintelligence capabilities in neighboring countries.