The word ‘expression’, when applied to music, has a comfortably familiar ring to it. However, on careful scrutiny it turns out to be more elusive than one might think. Intrinsic to musical expression is the idea that within music there is something to be expressed, and that this might be reinforced (or undermined) by the performance strategies adopted. The issue becomes more complicated when one asks whether the ‘something’ in question equates to inchoate feeling, to apprehensible meaning or to both in variable proportions. This chapter reviews historical approaches to musical expression and argues that the concept of Werktreue still shapes much of our thinking and teaching in this area. This leads to a consideration of the respective roles of composer, performer and audience, generating a diagrammatic matrix which is progressively modified throughout the chapter. In its final, most dynamic version, the matrix proposes a ‘field of musical expression’ in which the roles of composer, performer and listener interact. The authors suggest that the time is ripe for more interdisciplinary research on musical expression, where a fusion of approaches—from music psychology and computing to performance studies and artistic research—may be the key to a deeper understanding.