This review examines recent research on groups and teams, giving special emphasis to research investigating factors that influence the effectiveness of teams at work in organizations. Several performance-relevant factors are considered, including group composition, cohesiveness, and motivation, although certain topics (e.g. composition) have been more actively researched than others in recent years and so are addressed in greater depth. Also actively researched are certain types of teams, including flight crews, computer-supported groups, and various forms of autonomous work groups. Evidence on basic processes in and the performance effectiveness of such groups is reviewed. Also reviewed are findings from studies of organizational redesign involving the implementation of teams. Findings from these studies provide some of the strongest support for the value of teams to organizational effectiveness. The review concludes by briefly considering selected open questions and emerging directions in group research.