The types, functions, sources and effects of musicians’ bodily movements have been studied in soloists’ live and recorded performances, to a lesser extent in their practice sessions and rehearsals, and in ensemble musicians’ rehearsals. The present study explored the effects of familiarity and expertise on singers’ and pianists’ bodily movements and eye contact in ensemble rehearsals. Two established singer-pianist duos rehearsed three songs in different combinations. Quantitative and qualitative analyses were undertaken. Bodily movement and eye contact were used to consolidate technical details, convey musical information and coordinate entries. Singers used gestures to reflect and support the technical production of the sound, as well as conveying information relating to the meaning of the lyrics or the expressive content of the songs, while pianists’ gestures and glances were primarily expressive and communicative. Performers used bodily movement and eye contact to a greater extent when rehearsing with familiar and same-expertise partners than new or different-expertise partners; furthermore a wider range of such behaviours was produced in familiar partnerships. While expertise and familiarity do seem to influence the use of gestures and glances the head movements of the unfamiliar student duo became increasingly co-ordinated, suggesting that synchronisation can occur relatively rapidly in new partnerships and supporting existing findings relating to entrainment.