Commons enjoy recognition as an alternative to the dichotomy of state and market. In contrast to liberal market theorists who frame the commons as resource-based, we build on alternative and critical conceptions that describe the commons as processual, social, and inherently relational. Our analysis adds to these accounts an articulation of the contemporary commons as “social infrastructure” in the urban spatial conditions where the social processes of commoning take place. We argue that the relational features of urban commons depend on social interactions and cross-sector partnerships in physical places that promote social cohesion, suggesting that the urban commons fold together the spatial and social in hitherto undertheorized ways. To theorize this relationship, we articulate the idea of the relational urban commons as sites of social interaction and relationship building—social infrastructure. This conceptualization suggests that the commons can be governed indirectly by enabling access, participation, and partnerships across sectors, fostering mixed uses and the provision of maintenance and repair. As a result, the commons are both maintained by and conducive to place-based cross-sector partnerships, anchored in place in ways that transcend resources, issues, and ownership.