If comparative histories are rare, part of the blame may fall on Prof. Peter Kolchin, because his "Unfree Labor" sets an extraordinary standard. Much of what he says about American slavery is a reprise of his own book by the same title, but readers new to the topic will gain from the treatment here. For me, his discussions of Russian serfdom were revelatory, and on their own justified the book's purchase.But what really sets the book apart is the dissection of the similarities and differences between these two contemporaneous institutions. This is an ambitious project, and Kolchin casts a vast net to carry it off. His analyses consider geography, agricultural markets, folk tales, the ratio of bondsmen to owners, and the rise of state power. He deftly examines the disparate origins of serf and slave populations -- the one an indigenous majority, the other a displaced minority. Kolchin often illuminates his comparisons with digressions on Brazilian and Caribbean slavery, which had characteristics intermediate between the American and Russian extremes. The book's thematic divisions ("The Masters and Their Bondsmen" and "The Bondsmen and Their Masters") nicely frame life for those on either side of the wall of privilege. Finally, although Kolchin necessarily takes a lofty and abstract view, anecdotes and quotations enliven almost every page.No review of "Unfree Labor" would be complete without mentioning what a fine model of historical presentation it is. Kolchin writes well, but he also appreciates how eloquent a well-crafted map or table of figures can be -- something that seems to elude far too many historians.