Many established markets are seeing a rise in alternative organizing models to dominant corporate structures, aimed at promoting sustainable change from the ground up. Collective entrepreneurship initiatives are arising as social activists seek to address sustainability challenges in their local communities through business means. Commensurate with the emergent nature of this phenomenon, I rely on qualitative studies of two examples of collective enterprise to inductively develop new theory in this nascent field of research. In particular, a study of Renewable Energy Source Cooperatives in the transitioning German energy sector puts forward new theory on how collective social entrepreneurship initiatives generate and sustain member participation. A study on Bio-Energy Village initiatives in the same market context develops theoretical insight into how such collective entrepreneurial ventures can move individuals to disrupt the extant institutional arrangements they have taken for granted. Collectively, these studies advance our understanding of how community-based, collective entrepreneurship can break with unsustainable consumption patterns of the past and generate unprecedented citizen involvement in change towards greater sustainability in established markets.