While the value of teamwork for promoting effectiveness in organisational settings is widely acknowledged, nearly a century of research on teamwork within organisational psychology suggests that there are real difficulties in achieving effective teamwork. In these two linked articles, research is reviewed on the problems for teams of personality factors, flawed decision making, excessive cohesiveness, and social loafing. The effect of interventions designed to improve team functioning is examined. In the second of the articles, the problems identified in team working generally are examined in primary care settings, by reference to detailed case studies in six primary health care teams. The barriers to teamwork in these settings are identified but ways of overcoming them, suggested by organisational psychological research, are outlined.