If "slavery" is defined broadly to include bonded child labor and forced prostitution, there are upward of 25 million slaves in the world today. Individuals and groups are freeing some slaves by buying them from their enslavers. But slave redemption is as controversial today as it was in pre-Civil War America. In Buying Freedom, Kwame Anthony Appiah and Martin Bunzl bring together economists, anthropologists, historians, and philosophers...