McMahon (history, Dartmouth; Happiness: A History) has produced an authoritative intellectual history of Western concepts of equality. Much ink has been spilled about inequality by Thomas Piketty, Walter Scheidel, Branko Milanović, and other scholars of economics, history, and philosophy, but McMahon’s book is a rare general study of the topic; it examines the ways in which humans across millennia have formed and reformed notions of equality that buttress exclusion and hierarchy. McMahon traces egalitarianism across prehistoric hunter-gatherer societies, ancient Greek democracies, Christian theologies, Enlightenment philosophies, the American and French revolutions, socialism, fascism, the United Nations, and the U.S. civil rights movement. He shows how equality typically went hand in hand with exploitation of outgroups, yet he also believes that equal rights are elusive but not illusory, despite mounting global disparities of income and wealth. He writes prosily and reprises timeworn theories, such as the existence of a universal Axial Age. The book concludes that equality depends upon assumptions of inequality, which can generate more disparities. VERDICT Sweeping and discerning. This book about equality rewards readers comfortable with a dense academic style.