This dissertation explores how the mathematical expression known as the Fibonacci series has contributed to the organisation of my own musical compositions. Three distinct aspects of the series are considered in detail: 1. The expansion and contraction of musical intervals as a reflection of the relationship between the constituent integers of the series. 2. The identification of pitches and quantity of bars as a musical expression of the Fibonacci ratios. 3. The overall musical structure as a reflection of the Fibonacci series, and its effect on the perception of music of an integrated, and organic character. The introduction discusses the relationship between my research into the Fibonacci series and its expression in my music. Chapter 1 emphasises the structuring of elements in Un bout de ciel au loin, Chapters 2 and 3 focus on the relationship between number and intervallic contraction and expansion in Trois études for piano solo and Concerto for Violin and Chamber Orchestra respectively. In Chapter 4, I demonstrate how Rêves Obscurs, and Harmonies Étendues, make use of the distribution of a melodic fragment to different instruments, alongside the interruption of the Fibonacci series by a second, discrete series. Chapter 5 questions the usefulness of rigorous maintenance of the series, and the impact of variations from the series on the tonality of a work, with reference to Cadavre Exquis for three voices and mixed ensemble, and Violin Concerto no.2. The last chapter raises different points of reflection on the Fibonacci series as a technique for organising musical material.