Being a group member is an integral part of our everyday lives. Groups may take on any form, from small teams to crowds, to mere labels for social categories, and the influence of a group context on the individual is manifold and far-reaching. This is reflected in the variety of theories that researchers have used to explain behaviour in groups. These theories quite often reflect an underlying evaluation of groups, from mindless and evil to focused and task-oriented. They also reflect the complexities of the setting under scrutiny as in the investigation of organisational systems. Most approaches to the study of groups have to come to terms with complex dynamics within those groups and, at the same time, with complex interactions between a group and its environment. In the end, our own impression of groups and group membership will always influence our preferences for particular models and explanations.