Abstract. The purpose of this paper is to advance the team dynamics and group development literatures by developing and testing a theoretical model of how affect shapes transitions in teams over time. Integrating the group transitions literature with theory and research on the mood-as-input theory, I propose that shared team mood influences the extent to which team members seek out and experiment with alternative ways of completing their work at different points in a team’s life. In the first half of the team’s life, when team members are relatively task-focused, I argue that team positive mood (i.e., a positively valenced affective state shared by team members at a given point in time) stimulates, whereas team negative mood (i.e., a negatively valenced affective state shared by team members) suppresses, exploratory search. At the temporal midpoint, however, when team members’ focus on performance heightens, team positive mood acts as a shutoff switch for search, leading to a decline in exploratory search over the second half of the team’s life. Team negative mood at the midpoint, on the other hand, leads team members to persist in exploratory search, even as a deadline draws near. A team’s trajectory of exploratory search over time, I propose, influences team performance such that it is highest when teams engage in high exploratory search early in the team’s life and decline in exploratory search over the second half of the team’s life. The results of a longitudinal, survey-based study of teams preparing for a military competition largely support my predictions.