Research since the 1980s has documented the overwhelming complicity of the German medical profession and German racial scientists in Nazi biopolitics. The key role of the human sciences in Nazi biopolitics led the historian Detlev Peukert to formulate the thesis that the “genesis of the ‘final solution’” can be attributed to the “spirit of science.” Taking its cue from this provocative claim, my research project identifies and grapples with a central paradox in the relationship between racial science and Nazi biopolitics: Even though German racial scientists were deeply complicit in Nazi biopolitics, there was considerable tension between racial science and the trajectory of Nazi biopolitics. Whereas the complicity of German racial scientists in Nazi biopolitics is now well-documented, my project examines the question of how exactly the scientific theories propounded by racial scientists related to Nazi biopolitics and to what extent racial science and the Nazi regime exerted mutual influence on one another. Instead of using “race” as an analytical category for understanding the Third Reich, I argue that “race” remained a diffuse concept whose competing and contested meanings in the Third Reich are in need of historical analysis. The major contribution of my project is to examine the interaction of two competitive processes that played out in the early years of the Nazi regime: namely, the competition between different racial theories within the fractious field of racial science, on the one hand, and the rivalry between different political actors seeking to gain control of Nazi eugenic and racial policy within a polycratic regime, on the other. My study examines key controversies in racial science and racial policy in order to demonstrate that during the Nazi regime’s early years both racial science and Nazi biopolitics were characterized not by coherence but by diversity, improvisation, competition, and conflict. Just as different racial scientists were jockeying to impose their conceptions of race or heredity on the Nazi regime, a handful of newly created party, state and SS agencies were in fierce competition to take control of Nazi eugenic and racial policy. The central chapters of my study analyze three controversies in racial science and racial policy over three key topics: whether “racial mixing” was beneficial or noxious; whether there was a “German race” or whether the German people was composed of different races; and over how broadly the forced sterilization program should be targeted. The analysis of these three controversies allows me to develop an intellectual map of the competing research paradigms and a political map of the competing party, state and SS agencies. By asking who sought alliances with whom, for what purpose, at what time, I seek to elucidate how both scientists and Nazi officials deployed competing conceptions of race for strategic purposes at different points in the development of the Nazi regime. My study concludes by demonstrating that in assessing the influence of racial science on policy one has to differentiate between different scientific fields and different areas of Nazi policy.