English summary: Why was the German working-class movement struggling against the rise of National-Socialism so easily defeated, whereas the French working-class movement, which was numerically and organizationally much weaker than its German counterpart, succeeded in mobilizing hundreds of thousands of workers against the radical right at the moment of a fascist threat? To answer this question, Joachim C. Haberlens study investigates the social and political practices within the working-class movement in Leipzig and Lyon at the end of the Weimar Republic and, respectively, the Third French Republic. At the core of the study are the role of trust and distrust in social and political movements, and the ambivalent consequences of the politicization of the working-class movement within its local context. The study draws on a broad variety of primary sources from archives in Leipzig, Berlin, Lyon, Paris, and elsewhere. Informed by everyday historical approaches, it creates a lively and multifaceted image of workers lives and grassroots politics in both cities. The comparative approach results in a careful analysis that identifies major differences that help explain the different outcomes of the working-class movements struggles. Leipzigs working-class movement, the study shows, was characterized by a deep-seated distrust, which was a major impediment for a successful mobilization against the Nazis. Furthermore, the politicization of the local working-class movement not only reproduced the conflicts between Social Democrats and Communists at the rank-and-file level, but also turned politics into a nuisance that made many workers turn away from politics altogether. In Lyon, by contrast, workers succeeded in overcoming existing distrust. In addition, the politicization of the working-class movement during the rise of the Popular Front (1934-36) had, at first, an integrative function. Yet, soon enough the overburdening of social practices like strikes with political meaning contributed to the decline of the Popular Front. German description: Weshalb unterlag die deutsche Arbeiterbewegung in ihrem Kampf gegen die Nationalsozialisten, wahrend es der zahlenmassig weitaus schwacheren Arbeiterbewegung Frankreichs gelang, im Moment einer vermeintlichen Bedrohung durch die radikale Rechte Hunderttausende fur einen antifaschistischen Kampf Arbeiter zu mobilisieren? Joachim C. Haberlen untersucht die sozialen und politischen Praktiken innerhalb der Arbeiterbewegung in Leipzig und Lyon am Ende der Weimarer Republik bzw. der Dritten Franzosischen Republik. Im Mittelpunkt stehen dabei die Bedeutung von Vertrauen und Misstrauen in politischen und sozialen Bewegungen sowie die ambivalenten Auswirkungen der Parteipolitisierung der Arbeiterbewegung im lokalen Rahmen.