A common assumption is that if we just put good people together, they will automatically develop into a strong team. Conversely, we assume that if we put a lot of low-performing people together, they will perform poorly. However, research tells us that it is not that simple. Teams are different from the sum of their parts, and they develop as they go. Scholars have been able to develop a well-accepted model that can help managers and employees build team effectiveness in the workplace: the Input-Mediator-Outcome (IMO) team effectiveness framework. This note provides an overview of the well-supported IMO model of team effectiveness.