Carl Nielsen (1865-1931) stands out as a composer who developed his own musical language. His compositional output presents a sharp contrast with his contemporaries at a time when the stylistic trends moved toward either non-Romantic or anti-Romantic aesthetic ends. In his Fifth Symphony, Nielsen's treatment of form, tonality, melody, rhythm, counterpoint, and orchestration is a process of continual unfolding. This strategic scheme also encompasses a broader procedure that serves to unify the entire symphony. The ultimate goal of this thesis is to demonstrate the unique features of Nielsen's compositional style and process through an examination of his Fifth Symphony. The preface begins with a biographical overview including Nielsen's childhood, early years, career, and life as a composer. It also provides insights into the significance of his Fifth Symphony in music history as well as how this particular work expresses his musical identity. There are four main sections in this thesis. Chapter one discusses melodic and interval structures, and further examines the composer's unique approach to motivic and thematic development. This construction and organicism in turn frees the symphony from the traditional limits of tonality and form. Chapter two focuses on Nielsen's treatment of tonality. In particular, it explores those processes by which Nielsen unfolds the tonal scheme of passages and further develops them into organically whole movements and an entire organic symphony. Chapter three presents the conception of form in Nielsen's Symphony No. 5 and the manner in which he merges the traditional sonata form with the four-movement symphonic plan and his own two-movement symphony. This leads to Chapter four, where the significance of Nielsen's instrumentation -namely his creation of colorful sonorities through the particular use of solo wind instruments as well as inventive combinations of instrumental sections- is examined. The thesis concludes with an examination of the importance of Nielsen's contribution to the world of symphonies. His achievement and influence as an innovative composer is evidenced by the new ground that he explored in his Fifth Symphony. This is followed by an appendix which draws connections between Franz Joseph Haydn and Carl Nielsen in terms of their: 1) similar music background, 2) creative use of percussion in the symphony, 3) treatment of thematic material, and 4) use of humor as a compositional device.