Through a series of three papers, this thesis explores identity processes in 52 teams, ranging from amateur volleyball teams in Italy through to elite-level Olympic, professional and military teams. Paper 1 takes a multilevel approach to social identification and team performance, demonstrating that when identification occurs across the whole team (i.e., team level identification) this predicts an increase in both perceived and actual team performance. Paper 2 uses motivated identity construction theory (MICT, Vignoles, 2011) as an integrative framework to explore why people identify with teams. In doing so, this paper helps resolve confusions about the relationship between “personal” and “group level” identity motives that have troubled social identity researchers for almost four decades. Paper 3 extends this theorising by investigating these identity processes in a unique sample of elite-level teams. A longitudinal multilevel approach is used throughout these three papers, enabling us to explore team level effects as well as making causal inferences regarding the direction of relationships between identity motives, team identification and team performance. An example of how this series of papers led to a team development tool implemented within Great Britain Olympic men's and women's hockey teams is discussed.