Socially innovative civil society initiatives are seen as promising to address societal and environmental problems such as those encountered in the transport sector. However, many social innovators struggle when it comes to growth and achieving broader system-level impact. These problems are often ascribed to challenges associated with organizational structures. This paper investigates the scaling process and organizational development of a European social innovation in the transport sector, Commons Cargo Bikes. Empirically, the study primarily builds on two quantitative surveys with initiatives and users as well as qualitative interviews with spokespersons of an overarching network. The results indicate that social innovations can provide important complements to technological and market-based innovations by providing alternative solutions that reach geographical regions and users not typically addressed by traditional services. Furthermore, the study highlights that rather formal structures can be necessary for successful social innovation networks at a certain point. As the present case study indicates, tensions associated with organizational changes might, however, be anticipated and addressed proactively by combining different organizational archetypes in one structure.