Key-words: organizations, teams, team effectiveness, cognition.

Teamwork is an important asset for the performance of organizations. This thesis contains an analysis of the effect of shared mental models and shared temporal cognitions – a common understanding about the important aspects of work – on team effectiveness over time. The findings suggest that when teams know what needs to be done, who does what, and when they need to do something, they achieve their goals efficiently by avoiding conflicts, learning from each other and translating team learning behaviors into team performance improvement. Importantly, teams need to have a shared understanding about teamwork from the beginning of the team lifecycle.