Teams have become increasingly popular in organizations (Devine, Clayton, Philips, Dunford, & Melner, 1999), and the issue of process loss in teams presents a persistent challenge to teamwork and team effectiveness (Karau & Williams, 1993). The present study addresses a basic issue in process loss; namely, team member motivation to contribute personal resources toward individual and team-level goals. This study identified three sources of motivation in teams: Task demands, team attributes, and member traits. Individual motivation increased with task difficulty, increased as deadlines approached, and declined overall with time on task. Team efficacy was positively associated with episodic increases in motivation over time, while cohesion was unrelated to motivation. Trait motivation was positively related, and psychological collectivism negatively related to individual motivation. This relationship persisted over the lifespan of the team. The results of this study have implications for understanding the unique and joint role of individual and contextual influences on team member motivation over time and experience.