Groups don't become teams because that is what someone calls them. Nor do teamwork values by themselves ensure team performance. So what is a team? How can managers know when the team option makes sense and what they can do to ensure team success? In this article, drawn from their recent book The Wisdom of Teams, McKinsey partners Jon Katzenbach and Douglas Smith answer these questions and outline the discipline that makes a real team. The essence of a team is shared commitment. Without it, groups perform as individuals; with it, they become a powerful unit of collective performance. The best teams invest a tremendous amount of time shaping a purpose that they can own. The best teams also translate their purpose into specific performance goals. And members of successful teams pitch in and become accountable with and to their teammates. The fundamental distinction between teams and other forms of working groups turns on performance. A working group relies on the individual contributions of its members for group performance. But a team strives for something greater than its members could achieve individually. In short, an effective team is always worth more than the sum of its parts. Katzenbach and Smith identify three basic types of teams: teams that recommend things--task forces or project groups; teams that make or do things--manufacturing, operations, or marketing groups; and teams that run things--groups that oversee some significant functional activity. For managers, the key is knowing where in the organization real teams should be encouraged. Team potential exists anywhere hierarchy or organizational boundaries inhibit good performance.(ABSTRACT TRUNCATED AT 250 WORDS)