Preparing large ensembles for performance involves musical, social, logistical and financial challenges of a kind seldom encountered in other forms of collective music-making. The conventional approach to meeting the challenges that arise during rehearsal is to appoint a single musical overseer, usually a conductor, whose ostensible role in musical preparation is to directly influence the musicians while working towards the creation of a musical product to be delivered in later performances. Rehearsal leadership, viewed from this perspective, moves predominantly in one direction, from conductor to ensemble. But such a perspective oversimplifies the conductor’s relationship with the ensemble, the relationships between the musicians, and the strategies that the latter must employ when working in large ensembles. Conceptualizing the ensemble as a complex system of interrelated components, where leadership and creative agency are distributed and developed through rehearsal to achieve what audiences assume to be a unified whole, yields new understanding of the work of large ensembles. This chapter examines these components of the creative process in orchestral and choral rehearsal and performance, the internal and external forces shaping and constraining that process, and the approaches that individual musicians and conductors could adopt in response to the changing contexts in which such creativity might be manifested.