John Jost, a social psychologist at NYU, synthesizes decades of research into why people defend social systems that disadvantage them. System justification theory explains that human beings have a psychological need to see the systems they live under as fair, legitimate, and natural, a need that operates alongside self-interest and group interest. This motivation helps explain why the poor sometimes oppose redistribution, why women sometimes endorse sexist beliefs, and why minorities sometimes internalize prejudice against their own groups. Jost traces how this theory developed from early observations about working-class conservatism through laboratory experiments and cross-cultural studies. He examines the psychological functions system justification serves: reducing anxiety and uncertainty, managing potential threats, and satisfying the need for shared reality with others. The book also explores the conditions under which system justification weakens, when people become willing to challenge rather than defend existing arrangements. Jost writes for general readers while maintaining scholarly rigor, providing both accessible explanations and technical details for those who want them. Readers will find here tools for understanding puzzling political phenomena, from why inequality persists to why social movements succeed or fail. Essential reading for anyone interested in the psychological foundations of politics and social change.