Organizations are increasingly becoming dynamic and unstable. This evolution has given rise to greater reliance on teams and increased complexity in terms of team composition, skills required, and degree of risk involved. Highreliability organizations (HROs) are those that exist in such hazardous environments where the consequences of errors are high, but the occurrence of error is extremely low. In this article, we argue that teamwork is an essential component of achieving high reliability particularly in health care organizations. We describe the fundamental characteristics of teams, review strategies in team training, demonstrate the criticality of teamwork in HROs and finally, identify specific challenges the health care community must address to improve teamwork and enhance reliability.Key Words. High-reliability organization, teams, teamwork, health care, patient safety, training A healthy 38-year-old woman was admitted to a major medical center to deliver her first child. Although she was a low-risk patient with only mildly elevated blood pressure, her admission ended tragically when she underwent an emergency cesarean after a failed forceps delivery. Once inside the abdominal cavity, the uterus was found to have ruptured, and the placenta was in the abdomen. She delivered a stillborn fetus. After an unsuccessful attempt to repair her uterus, she received a full hysterectomy, underwent blood transfusions, and endured endless complications resulting in a 3-week hospital stay, including 18 days in intensive care. What went wrong? According to root cause analyses, lack of teamwork played a significant role. Specifically, communication was poor; there was a lack of mutual performance cross-monitoring, inadequate conflict resolution, poor situational awareness, and work overload. A major response to the tragedy was the initiation of team training at the medical center (Sachs 2005).