Cities have always been a critical space of experimentation. The urban commons transform cities around the globe through projects and practices that challenge capitalist accumulation, extraction, and enclosure. Together, they give shape to a political proposal that requires the invention of new kinds of institutions, spaces, and actors responsible for their production and reproduction. The Urban Commons Research Collective offers this handbook – a compilation of definitions, experiences, and references – as a way to address some of the questions that arise when thinking about the urban commons as open organisational systems for collective management.