This dissertation explores the interactions between non-market entrepreneurs (e.g., activists and homeless services organizations) and public policy in the fight against homelessness. In the first chapter, I investigate how public support alters non-market organizations' behavior. I draw on the emerging literature on organizational sponsorship to understand how public support affects the diffusion of a new homeless shelter model. I find that public funding alters the non-market entrepreneurial process, leading organizations to radically change their approach to homelessness by adopting the government's preferred shelter type in lieu of traditional or alternative programs. The second chapter asks why the government came to support innovation in homeless services in the first place. I synthesize insights from several core strands of entrepreneurship theory to provide a theory of public entrepreneurship that explicitly considers the role of evidence in the policy process. I apply this theory to explain how a complex process of public entrepreneurship involving activists, experts, and policymakers gave rise to a shift in homelessness policy in the United States at the turn of the 21st century. The final chapter asks whether federal homelessness funding reduced homelessness in communities in the period I study. I find that communities that receive greater funding have higher rates of "sheltered" homelessness (people housed by homeless services organizations); however, they do not actually have lower rates of "unsheltered" homelessness (people sleeping outside). This finding suggests a tenuous link between non-market organizations, policy change, and people experiencing homelessness---highlighting some of the limits on the government's ability to "guide" the entrepreneurial response to complex social problems.