The story of Rachmaninoff's life and career is perhaps one of the most unusual among those of famous composers. Not only did Rachmaninoff live in two centuries, experiencing many changes in music, literature, theatre and art, but he also witnessed momentous changes in Russia, as well as the impact of world events on Russian history: the end of the Tsar's Russia with the Revolution of 1917 and the First and Second World Wars. Numerous identified and unidentified sources have called Rachmaninoff "the last Romantic of the twentieth century," implying that his style remained firmly in the Romantic tradition throughout his career, untouched by twentieth century musical unfluences. In fact, though, his style did evolve, but it did so in ways whoch were so smooth and subtle that the changes were alamost unnoticed. This dissertation project focuses on the evolution of Sergei Rachmaninoff's musical style as illustrated by his four Piano Concertos and the Rhapsody on a Theme by Paganini, comparing different stylistic features such as orcherstration, harmonic and melodic language, and the relationship between the piano and the orchestra. The writer used piano and orchestra scores of Rachmaninoff's four piano concertos and the Rhapsody on a Theme by Paganini, as well as on many recordings of these works, books and many released research works which are currently available.