The monograph explores the history of the Social Democratic Party of Germany during the years of the fascist dictatorship (1933-1945), its ideological and political evolution. Characteristics of various ideological and political movements in the SPD, its left and right wings are given; the activities of the German Social Democracy in exile and in the German underground are considered. At the center of the study is the struggle of trends in the SPD on the problems of anti-fascist tactics, primarily on the problem of a single worker and anti-fascist popular front. For historians, propagandists.