This dissertation was a sociological analysis of Proposition 71, The California Stem Cell Research and Cures Act in 2004. Using the conceptual domains of biomedicalization and science & technology studies, my research examined the emergence of health social movements within the fields of regenerative medicine, as well as the debates around the reification of human biological objects. The narrative arc of this dissertation begins with the drafting of Prop 71, through the initial implementation of the California Institute for Regenerative Medicine, the organization created by Prop 71. This project was animated by two central research questions. First, what are the institutional contexts and processes through which regenerative medicine is becoming a legitimate form of medicine? In my dissertation, I approached this question by examining the lineages of regenerative medicine in the biomedical and biological sciences. Second, what are the on-going, enduring effects of the intersections between controversial sciences and forms of biological citizenship? I developed the concept of "biomedical counterpublics" as a lens to examine the forms of social organization in and around human stem cell research. I conducted participant observation of the Yes on 71 Northern California field campaign, as well as interviews with activists (both in support and in opposition to Prop 71), campaign staff, and bench researchers who worked on behalf of the campaign, and textual analyses of campaign documents. These data revealed the contours of collective identities formed around diseases or conditions that could be ameliorated by stem cell technology, as well as the institutional transformations that have brought biomedical scientists into varied relationships with different publics. This research does not critique regenerative medicine as a new form of instrumental rationality or technological domination or slippery slope. Rather, I argue stem cell research is taking shape both within existing institutional situations, both in terms of research agendas as well as other lines of work, and simultaneously producing new forms of affiliation and political representation. In this sense, regenerative medicine marks sets of practices and institutions that are productive of new forms of attachment, as well as new modes of exclusion.