Spheres of Justice, with the subtitle "In defence of pluralism and equality", is the title of a book written by Michael Walzer.

In it, Walzer argues in favour of an idea he calls "complex equality", and against the view that goods with different meaning and content can be lumped together into the larger category of primary goods, as is advocated by John Rawls, in his A Theory of Justice from 1971. The book might be considered an attempt, from a liberal starting point, to bridge some of the disagreements between liberals and communitarians in political philosophy.

Michael Walzer (3 March 1935) is one of America's leading political philosophers. He is a professor emeritus at the Institute for Advanced Study in Princeton, New Jersey and editor of Dissent, a left-wing quarterly of politics and culture. He has written on a wide range of topics, including just and unjust wars, nationalism, ethnicity, economic justice, social criticism, radicalism, tolerance, and political obligation. He is also a contributing editor to The New Republic and a member of the editorial board of Philosophy & Public Affairs. To date he has written 27 books and has published over 300 articles, essays, and book reviews. He is a member of several philosophical organizations including the American Philosophical Society.

Michael is the older brother of historian Judith Walzer Leavitt.

Walzer is usually identified as one of the leading proponents of the "Communitarian" position in political theory, along with Alasdair MacIntyre and Michael Sandel. Like Sandel and MacIntyre, Walzer is not completely comfortable with this label. He has, however, long argued that political theory must be grounded in the traditions and culture of particular societies and opposed what he sees to be the excessive abstraction of political philosophy. His most important intellectual contributions include a revitalization of just war theory that insists on the importance of ethics in wartime while eschewing pacifism; the theory of "complex equality," which holds that the metric of just equality is not some single material or moral good, but rather that egalitarian justice demands that each good be distributed according to its social meaning, and that no good (like money or political power) be allowed to dominate or distort the distribution of goods in other spheres; and an argument that justice is primarily a moral standard within particular nations and societies, not one that can be developed in a universalized abstraction.

In April 2008, Walzer received the prestigious Spinoza Lens, a bi-annual prize for ethics in The Netherlands.