This groundbreaking book provides a comprehensive and compelling introduction to the field of leadership that is jam-packed with theoretical and practical insights derived from a wealth of applied scientific research conducted by the authors and their colleagues around the world over the last four decades. The book starts from the premise that leadership is never just about leaders. Instead, it is about leaders and followers who are joined together as members of a social group that provides them with a sense of shared social identity. Leadership is understood as the process through which leaders work with followers to create, represent, advance, and embed this sense of shared social identity. The new edition of this bestselling book captures the breadth and depth of ongoing research from around the world that speaks to the power of social identity as a basis for both effective leadership and engaged followership. This approach is highlighted in case studies from the COVID-19 pandemic and as a way of understanding the rise, fall and resurgence of Donald Trump. The book also discusses practical applications that show how leaders can create, advance, represent and embed social identity in ways that are beneficial not only for group engagement and performance but also for health and well-being. Drawing on real-world examples and rich data sources, this book will appeal to academics, researchers, and students of psychology, business, and management, as well as to practitioners, policy makers, and anyone interested in the workings of leadership, influence, and power.