It is impossible to understand human behavior without understanding the critical role that groups play in people’s lives. Most of us belong to a range of formal and informal groups, including families, work teams, and friendship cliques. These groups absorb a great deal of our time and energy and are instrumental in satisfying our most fundamental needs. In addition, they connect us to larger social aggregates (e.g., political parties, business organizations, religious denominations) that influence our lives in important ways.This volume provides a comprehensive overview of classic and contemporary issues in the field of group processes. Chapters are written by internationally known experts who have made major theoretical and empirical contributions to the study of groups. The broad and up-to-date coverage of the book makes it an essential resource for advanced undergraduates, graduate students, researchers, and practitioners. The volume will be of interest to scholars in various disciplines, including social and organizational psychology, sociology, communication, economics, and political science.