In this paper we argue that recent developments in peer-to-peer platforms, including those underpinned by distributed-ledger technology (or blockchains), represent a new model for organizing collective action, which we term the “marketized-commons” model. Drawing on social psychological and economic theory, we compare this concept to established modes of organizing collective action. We also consider the marketized-commons model in relation to other peer-to-peer economies. We consider why individuals might be motivated to create and use platforms underpinned by the marketized-commons model, as well as how it might be counterproductive for cooperation, collaboration, participation and social goals. Finally, we recommend implications for those interested in designing peer-to-peer platforms to support collective action. Ultimately, we argue that to develop effective platforms in this context designers need to look beyond the financial considerations of individual platform users. Rather, they also need a concern for social psychological principles and processes, specifically how groups work and operate in these settings.