This Article: explores patterns of legal-institutional change in the emerging, platform-driven economy. Its starting premise is that the platform is not simply a new business model, a new social technology, or a new infrastructural formation (although it is also all of those things). Rather, it is the core organizational form of the emerging informational economy. Platforms do not enter or expand markets; they replace (and rematerialize) them. The article argues that legal institutions, including both entitlements and regulatory institutions, have systematically facilitated the platform economy's emergence. It first describes the evolution of the platform as a mode of economic (re)organization and introduces the ways that platforms restructure both economic exchange and patterns of information flow more generally. It then explores some of the ways that actions and interventions by and on behalf of platform businesses are reshaping the landscape of legal entitlements and obligations. Finally, it describes challenges that platform-based intermediation of the information environment has posed for existing regulatory institutions and traces some of the emerging institutional responses.