Melody is a fundamental concept in Western musical thought; it connotes the form and affective power of successive sounds in motion, perceived as an aesthetic unity. Yet for many writers, melody does not exist as an autonomous form, and for those who credit its existence, few agree on what it is, or how it functions in relation to harmonic voice leading and phrase rhythm. This chapter examines the historical emergence of a theory of melody in the West, from Aristoxenus to Leonard Bernstein; it traces the rich intellectual currents that saw melody variously coupled to ideas of voice, schemes of rhythmic symmetry, overtones, spatial organization, theories of evolution, and computational analysis.