This thesis explores the phenomenon of the piano accompanist in Western art duo chamber ensembles, specifically the solo–accompaniment medium. Following a critical examination of relevant literature by practitioners and researchers where changing socio-cultural attitudes towards accompanists are discussed along with related issues about accompaniment and ensemble playing more broadly, two empirical studies are reported. These enquiries aim to investigate the expectations of contemporary professional soloists and pianists about accompanists as well as to explore the skills and roles exhibited by pianists working in the solo–accompaniment duo context, which have yet to be systematically evaluated. Both studies adopt qualitative methodology with interpretative phenomenological analysis, the first comprising interviews with twenty professional musicians, the second involving case study observation of rehearsals and performances using video recalls with three accompanists and three soloists working in different combinations. The data provided insight into the range of musical and other expectations articulated by professional musicians about piano accompanists as well as the nature of the skills and roles involved in achieving ensemble, interpreting soloists’ intentions, dealing with unexpected incidents, achieving balance and communicating with soloists. A novel conceptual framework about accompaniment practice is constructed based upon the data from the two studies as well as the relevant literature which articulates musico-functional and socio-emotional aspects of accompaniment practice.