Michael Walzer is one of the world's most important political thinkers, whose major works, such as Spheres of Justice and Just and Unjust Wars, have transformed many central debates in contemporary political philosophy. In this book, Toby J. Reiner provides the most wide-ranging and up-to-date introduction to his work available. Reiner examines his writings on topics ranging from justice in war, humanitarian intervention and migration ethics to distributive justice, multiculturalism, and the political role of religion. Situating Walzer's thought in the intellectual environment of post-war American leftist politics, Reiner demonstrates the importance of his attempt to provide a social-democratic alternative to liberalism, Marxism, and post-modernism. He shows that Walzer has developed a novel approach to political theory based on the thesis that human communities construct the values that give meaning to their lives, giving his work a significance that goes well beyond political theory, into political and social science more broadly. Reiner not only gives a crystal clear guide to Walzer's ideas for students of political philosophy and general readers, but also develops an original and illuminating new interpretation of his thought that no political theorist can afford to miss.