Social structures determine who has power and influence, account for why people fail to assimilate basic facts, and enlarge our understanding of patterns of contagion—from the spread of disease to financial crises. Despite their primary role in shaping our lives, human networks are often overlooked when we try to account for our most important political and economic practices. Ranging across the disciplines of psychology, sociology, and business, Matthew Jackson brilliantly illuminates the complexity of the social networks in which we are—often unwittingly—positioned, and unpacks why we are who we are, and why we succeed or fail.