Groups are a key part of human experience. Whether the group is a family, a street gang, a work group, an ethnic minority or a network of friends, group membership and influence represents one of the most powerful forces shaping our feelings, judgements and behaviours. While group processes can lead to aggressive and destructive outbursts, so too are they a source of love, achievement, nurturance, loyalty and sacrifice. In this book the authors share the excitement and challenge of conducting research on groups. They familiarize the reader with the theoretical perspectives and data that provide us with the means of interpreting group phenomena. They place special emphasis on several aspects of group experience that they feel are particularly significant: social influence, group productivity, group decision-making, and intergroup conflict and prejudice; and they explore the significance for the application of group theory in our everyday lives.