In an age when most intellectuals swing mercurially back and forth between conversion and cynicism, Michael Walzer incarnates the integrity and dedication of the eighteenth-century philosophes. Walzer has participated in every important political struggle of the past quarter century, as both a thinker and an activist, fighting for the rights of blacks, of women, of poor people, of Vietnamese, of Israelis and Palestinians. Walzer, a professor of social science at the Institute for Advanced Study in Princeton, is the author of The Revolution of the Saints, Obligations, Just and Unjust Wars, Radical Principles, and, most recently, The Spheres of Justice. His best writing has generally grown out of concrete political conflict. But his work has a solidity and depth that should outlive the struggles that have inspired it. If words like justice and humanity have any real meanings in the late twentieth century, Walzer may be the man who can tell us what they are.