The Faustian bargain-in which an individual or group collaborates with an evil entity in order to obtain knowledge, power, or material gain-is perhaps best exemplified by the alliance between world-renowned human geneticists and the Nazi state. Under the swastika, German scientists descended into the moral abyss, perpetrating heinous medical crimes at Auschwitz and at euthanasia hospitals. But why did biomedical researchers accept such a bargain? The Nazi Symbiosisoffers a nuanced account of the myriad ways human heredity and Nazi politics reinforced each other before and during the Third Reich. Exploring the ethical and professional consequences for the scientists involved as well as the political ramifications for Nazi racial policies, Sheila Faith Weiss places genetics and eugenics in their larger international context. In questioning whether the motives that propelled German geneticists were different from the compromises that researchers from other countries and eras have faced, Weiss extends her argument into our modern moment, as we confront the promises and perils of genomic medicine today.