The paper presents an overview of the unique structure and complexity of sport teams. It provides the reader with general and basic information about both, the physiological and psychological structure of sport teams. It describes the unique characteristics of interpersonal relationships in sport teams, and provides information on how individual capabilities and motivational processes might influence group performance. In this context, particular attention is paid to specific models that examine group processes and interaction. In addition, it illustrates the consequences of social influence on group interaction and performance. Finally, the paper provides an outlook to future tendencies of group dynamics and the importance of interpersonal relationships in sport groups.