Johann Friedrich Blumenbach was one of the most celebrated practitioners of natural history of his generation, who from 1776 till the year of his death taught in the medical faculty of the University of Gottingen. Internationally, Blumenbach's significance is commonly narrowed down to his work on human skulls. The Cambridge Biographical Encyclopedia offers no more than the following single and incorrect sentence: "By his study of comparative skull measurements, he established a quantitative basis for racial classification". The Blumenbach identity to which we are contributing is a contested, fractured one and, for the first time, the product of professional historians of science and medicine. A broader set of interests, questions, and fields of expertise than before is brought to bear on his physical anthropology. The chapter addresses largely unanswered questions, such as: how exactly did Blumenbach define race and races? and What were his scientific criteria?