This paper asks how entrepreneurs organize, and how they come to be organized in communities. The paper reviews literature on regional entrepreneurial networks and organizing in incubators, and finds that prior research has alluded to the role of communities, but neglected to develop explicit theory on the origins of meso-level social structures. To build such theory, in-depth case study data (including 119 interviews with 133 participants) were collected during field studies in Kigali, Harare, and Accra from September-December 2014. Six entrepreneurial communities anchored in local coworking spaces are used as comparative case studies. The paper finds that coworking spaces are unique organizational actors, in that they enable community formation by working as social enclosures, locational fix points, and symbols of a purpose. Based on within-case process tracing and cross-case pattern matching, the paper then theorizes the assembly process: coworking spaces assemble previously distant and different actors into entrepreneurial communities. Assembly consists of three mechanisms: convening (creating occasions for interactions), interconnecting (matching complementary actors), and activating (stimulating mutual concern among community members). Assembly theory highlights the need for more studies of entrepreneurial organizing processes, and addresses important meso-level theory gaps in research on the coordination and organization of entrepreneurship.