This book presents a compelling argument that the Western Church's marriage and family policies, which emerged during the early Middle Ages, played a crucial role in fostering the development of Western societies. By promoting nuclear families, monogamy, and prohibiting incest and cousin marriage, these policies inadvertently led to the breakdown of kin-based institutions and the promotion of individualism, trust, and cooperation with strangers. The author, an interdisciplinary scholar, uses a wealth of historical and empirical data to show how these unique marriage and family norms contributed to the rise of impersonal markets, democratic governance, and innovation. This transformative shift, the book argues, is what set Western societies on a distinct path of development, characterized by peculiar psychology, behaviors, and social dynamics that have had profound global impacts.