At the end of the 19th century, the socialist parties of the Second International experienced a profound identity crisis known as the Revisionist Dispute. This teach-in explores the particular manifestation of Marxism’s crisis in France through the Millerand Affair and situates it within the context of the Second International. How did the orthodox Marxists understand the emergence of revisionism? What did it mean to recognize opportunism as both a regression and a possibility? What is the legacy of the Second International today?