As we move through the 21st Century, a variety of chamber music ensembles emerge. More unconventional ensembles are appearing, and the rationale of an ensemble's aim or output is becoming more concentrated. No longer can a group be described simply as an 'early music ensemble' or 'new music ensemble', but to find a niche in the ever growing number of small to medium groups, ensembles are becoming more definitive by nature. Through developing a unique approach to performance practice, group identity, and audience perception, the ways in which an ensemble prepares for a performance is determined by a number of aspects. This paper explores repertoire choice as a contributing factor to the successful operation of a chamber music ensemble. Part of a larger study on the processes of chamber music ensembles, this paper focuses on the life experiences of three professional chamber musicians actively involved in chamber music performance, and specifically focuses on the functions and meaning of a group's repertoire choice in the creative and organizational process of a musical group. The study uses a qualitative framework and Interpretative Phenomenological Analysis of three semi-structured interviews as case studies to analyze and describe the meaning of the impact repertoire has on group process, aims and performance. The findings identify the key functions of repertoire choice from a performer and audience perspective including the functionality of the ensemble, verbal and non-verbal communication between players and audience, and the artistic goals and outcomes of the group. The study highlights the sociological importance of the relationship between repertoire and group process, and the need for practicing musicians to fully understand the significance this has on the success of an emerging and/or established ensemble.