The French composers Tristan Murail (b.1947) and Gerard Grisey (1946-98) are the two chief originators of “Spectral Music”, an approach to composition that developed in France from the mid-1970s, and which is characterised by the ‘spectrum’, a conception and codification of sound as a collection of individual, related partials, realised by orchestral synthesis. While the composers’ exploitation of the physical characteristics of sound, based on technological analysis, is well documented, Murail has drawn analogies throughout his mature work with other phenomena, including those associated with electroacoustic means of sound treatment and production, morphologies found in the earth’s surface (both land and water) and recently developed scientific paradigms (chaos theory and fractal geometry). In Murail’s most recent works, the complex properties of sound samples are used as compositional models. The application of these analogies is diverse, ranging from the use of relatively simple algorithms to the formation of elaborate structures that possess a highly evocative and metaphorical mode of communication. The use of inharmonic sounds, or “noise”, in particular, evokes nature and places the work in a particular relationship with the world. The thesis investigates the appropriation of phenomena by analogy through analysis of key compositions. While research focuses on Murail, the work will be contextualised alongside that of Grisey, and within Spectral Music in general, in order to gain a greater critical understanding of the music