Organizations invest in teamwork as it can be an effective way of organizing work and to achieve overall goals. A team differs from other groupings in task interdependence, reflexivity on performance, shared objectives and boundedness, and not all tasks are suitable for teamwork. Routine tasks, little autonomy, and a low degree of task interdependence make teamwork obsolete. It is not always that teams are effective, and it takes a multi-level approach to explain and enhance team effectiveness. The Input-Mediator-Outcome-Input (IMOI) model describes processes as mediators between inputs and outcomes. Important inputs are individual characteristics and KSAOs, team composition, team characteristics, task design as well as organizational support. Leadership processes, as well as cognitive, emotional and behavioural team processes play a crucial role as mediators. The expected outcomes of effective teamwork are learning and growth for the individual, team learning and viability, and results related to organizational objectives, e.g. efficiency and innovation.