The book focuses on the concepts of expertise, personality, cohesion (group cohesion), and performance, which are integrated into a model of performance-related interaction among music groups from the perspective of the social psychology of music-making through the examination of five bands. The work is characterized by new and adapted methodological approaches and a continuous discussion of methods, as it discusses approaches from psychology in relation to their applicability in musicology. The result is an expanded concept of expertise and the realization that the necessary social and organizational competencies for successful group music-making must be developed. For practitioners, the book offers insights and raises awareness to consider group interactions in a nuanced way and to evaluate group performances in a differentiated manner.