Book excerpt: In an in-depth comparative analysis, Stefano Bartolini studies the history of socialism and working-class politics in Western Europe. While examining the social contexts, organizational structures, and political developments of thirteen socialist experiences from the 1860s to the 1980s, he reconstructs the steps through which social conflict was translated and structured into an opposition, as well as how it developed its different organizational and ideological forms, and how it managed more or less successfully to mobilize its reference groups politically.