Who are the Jews—a race, a people, a religious group? For over a century, non-Jews and Jews alike have tried to identify who they were—first applying the methods of physical anthropology and more recently of population genetics. In Legacy, Harry Ostrer, a medical geneticist and authority on the genetics of the Jewish people, explores not only the history of these efforts, but also the insights that genetics has provided about the histories of contemporary Jewish people. Much of the book is told through the lives of scientific pioneers. We meet Russian immigrant Maurice Fishberg; Australian Joseph Jacobs, the leading Jewish anthropologist in fin-de-siècle Europe; Chaim Sheba, a colorful Israeli geneticist and surgeon general of the Israeli Army; and Arthur Mourant, one of the foremost cataloguers of blood groups in the 20th century. As Ostrer describes their work and the work of others, he shows that to look over the genetics of Jewish groups, and to see the history of the Diaspora woven there, is truly a marvel. Here is what happened as the Jews migrated to new places and saw their numbers wax and wane, as they gained and lost adherents and thrived or were buffeted by famine, disease, wars, and persecution. Many of these groups—from North Africa, the Middle East, India—are little-known, and by telling their stories, Ostrer brings them to the forefront at a time when assimilation is literally changing the face of world Jewry. A fascinating blend of history, science, and biography, Legacy offers readers an entirely fresh perspective on the Jewish people and their history. It is as well a cutting-edge portrait of population genetics, a field which may soon take its place as a pillar of group identity alongside shared spirituality, shared social values, and a shared cultural legacy.