Thanks to large families, a retention rate that approaches 80%, and anti-modern beliefs and practices that privilege community, tradition and mysticism, the number of hassidim has increased to about 350,000 in North America, 445,000 in Israel, and 100,000 in other places around the world.Hassidic communities have survived – and thrived – despite (and because of) the threats posed by Nazism, Soviet communism, geographical dislocation, secularism, assimilation and the death of charismatic leaders.In Who Will Lead Us?: The Story of Five Hasidic Dynasties in America, Samuel C. Heilman, a professor of Jewish studies and sociology at Queens College, City University of New York, and the co-author of The Rebbe: The Life and Afterlife of Menachem Mendel Schneerson, sets the context for the revival by explaining how succession in five hassidic “courts” has been handled: the Munkács and Boyan (where no obvious successor presented himself); Bobov and Satmar (where competing successors emerged); and Chabad/Lubavitch (where hassidim “solved” the problem of succession by denying that their rebbe was really gone). Filled with fascinating details, Who Will Lead Us? illuminates the world of contemporary hassidim.Although the role of the chief hassidic rabbi has not been formalized, Heilman points out, it is clear that he is essential to the identity and loyalty of his followers. This bond has led to an acceptance of dynastic succession. However, Heilman demonstrates that personality, ambition, social and political skills and familial relationships – as well as birth order – help determine the outcome.Heilman lays out a few “central lessons” of succession. Careful scholar that he is, however, he acknowledges that these generalizations do not always apply. Being anointed by the leader (as were Naftali Halberstam, the fourth Bobover rebbe, and Yosef Yitzchak Schneerson, the sixth Lubavitcher rebbe), Heilman asserts, makes the heir apparent a prohibitive favorite, “even when he was not the ideal candidate for the role everyone expected him to take.”In the absence of an explicit endorsement, wills frequently appeared, disappeared, and had their authenticity challenged. The wives of rebbes sometimes intervened to advance the candidacy of their favorite sons (or sons in law).Charisma helps a new rebbe persuade his flock that, like his predecessor, he possesses otherworldly powers. To be sure, Heilman notes, charisma often lies in the eyes of the beholders – and winning a contest for succession can endow a new leader with a personality trait that was heretofore not all that visible. During divisive succession contests, Heilman suggests, hassidim often give voice to a belief in the imminent Messiah (an event that would, of course, render the outcome of the contest irrelevant). The hassidic belief in the decline of the generations, he emphasizes as well, necessarily valorizes the old over the new and predecessors over successors. Nonetheless, in the late 20th and 21st centuries, rebbes have drawn on allies with deep pockets, the welfare state and social media to increase their influence locally and globally.Heilman’s conclusions about succession are valuable. His accounts of the escape of several hassidic rebbes from the Nazis are riveting. Singled out as targets, these men exhibited extraordinary courage. Although he had shaved his beard and cut his earlocks to escape capture, Shlomo Halberstam, the third Bobover rebbe, conducted secret gatherings in Poland at Shabbat’s end, after curfew, where he offered “hushed words of Torah, hassidic teaching, and spiritual encouragement.” He arranged for Naftali, his son, to sail to Turkey and then Palestine, before trying to save himself.Heilman also demonstrates, however, that the rebbes would not have survived without the financial assistance of supporters (who bribed officials to free them from Gestapo custody and secure forged documents to get them out of Eastern Europe) and of Zionists (whom hassidim had regarded as mortal enemies). Their experiences during World War II reinforced the conviction of their followers in North America and Israel in the 1940s and ’50s that God had chosen them to secure the future of their people.These days, Heilman reminds us, hassidim have set aside their reservations about the United States and Israel, concluded that redemption may not be imminent, and with a sense of confidence “perhaps unprecedented in their history,” they have built cohesive, durable (and often politically potent) urban communities.Even post-Soviet Russia, Heilman notes, has a fair share of hassidim. Wherever they reside, and no matter how “disenchanted” they are with the environment that surrounds them, hassidim continue to see their rebbe as a source of identity, blessings and strength, endowed by God with miraculous or extraordinary powers.They organize their lives “so that they may be near him or at least in touch with what he wants.” For these reasons, Heilman concludes, hassidim do not take the relationship (or the need for “repeated reanimation” of that relationship) for granted. And so, the question of who will succeed their leader remains as urgent – and perhaps even more urgent – than ever. Glenn C. Altschuler is the Thomas and Dorothy Litwin Professor of American Studies at Cornell University.