This book explores the political implications of the human tendency to prioritize negative information over positive information. Drawing on literatures in political science, psychology, economics, communications, biology, and physiology, this book argues that 'negativity biases' should be evident across a wide range of political behaviors. These biases are then demonstrated through a diverse and cross-disciplinary set of analyses, for instance: in citizens' ratings of presidents and prime ministers; in aggregate-level reactions to economic news, across 17 countries; in the relationship between covers and newsmagazine sales; and in individuals' physiological reactions to network news content. The pervasiveness of negativity biases extends, this book suggests, to the functioning of political institutions - institutions that have been designed to prioritize negative information in the same way as the human brain.