Guilds ruled many European crafts and trades from the Middle Ages to the Industrial Revolution. Each guild regulated entry to its occupation, requiring any practitioner to become a guild member and then limiting admission to the guild. Guilds intervened in the markets for their members’ products, striving to keep prices high, limit output, suppress competition, and block innovations that might disrupt the status quo. Guilds also acted in input markets, seeking to control access to raw materials, keep wages low, hinder employers from competing for workers, and prevent workers from agitating for better conditions. Guilds treated women particularly severely, usually excluding them from apprenticeship and forbidding any female other than a guild member’s widow from running a workshop. Guilds invested large sums in lobbying governments and political elites to grant, maintain, and extend these privileges. Guilds had the potential to compensate for their cartelistic activities by creating countervailing benefits. Guild quality certification was one possible solution to information asymmetries between producers and consumers, which could have made markets work better. Guild apprenticeship had the potential to solve imperfections in markets for skilled training, and thus to encourage human capital investment. The cartel profits generated by guilds could in theory have encouraged technological innovation by enabling guild masters to appropriate more of the social benefits of their innovations, while guild journeymanship and spatial clustering could diffuse new technical knowledge. A rich scholarship on European guilds makes it possible to assess the degree to which guilds created such benefits, outweighing the harm they caused. After about 1500, guild strength diverged across Europe, declining gradually in Flanders, the Netherlands, and England, surviving in France and Italy, and intensifying across large tracts of Iberia, Scandinavia, and the German-speaking lands. The activities of guilds contributed to variations across Europe in economic performance, urban growth, and inequality. Guilds interacted significantly with both markets and states, which helps explain why European economies diverged in the crucial centuries before industrialization.