["The British Journal of Sociology, EarlyView. ", "\nAbstract\nThis study is designed to remedy the tendency of existing studies to analyze online marketplaces as either sites of work or trading arenas. We argue that the theoretical notion of “social infrastructure” is particularly apt to offer a comprehensive framework that captures the unique intersection of work and trade in online marketplaces. We study the social infrastructure of an online marketplace: the institutions, conditions and forms, and the horizontal and vertical ties between actors that organize work and enable trading. The social infrastructure of online marketplaces deserves research attention because it represents an essential condition for economic activities. In our empirical section we focus on the online marketplace Etsy to illustrate our comprehensive theoretical framework and we identify a complex dynamic between the decided and emergent order of the online marketplace. We demonstrate that the attempt to superimpose order through the constitution of an online marketplace is challenged by sellers and buyers. We find that both dimensions, work and trade, provide actors with material and symbolic resources that inform their strategies and economic actions. The article suggests that “social infrastructure” is a concrete theoretical tool for analyzing online marketplaces that complements existing research on platforms and ecosystems.\n"]