Online platforms have a growing influence on how people interact with the physical world. They organise data streams, economic interactions and social exchanges of their users. Competitive dynamics in this emerging ‘platform society’ revolve around the ability to attract users to a platform, and to collect and analyse data from their interactions to achieve network effects. This chapter is about the roles of online platforms in enabling a more sustainable and circular economy. It identifies and describes three potential roles: they can enable people and organisations to (1) market, (2) operate and (3) co-create products, components and material. The identified roles provide a playground for firms to experiment with online platforms to advance their digital transition towards a circular economy.