Polish composer, Karol Szymanowski (1882-1937) wrote a substantial number of piano works from 1899-1934, yet these works have been mostly forgotten or ignored outside his country. Szymanowski scholars divide his works into three periods. The second period represents the most radical shift in his compositional style particularly in his treatment of form, harmony and texture. This study demonstrates the musical and historical influences evident in his Piano Sonata No. 3, Op. 36 (1917), the last piano work written during his second period. Piano Sonata No. 3 exhibits elements of two contrasting styles, French Impressionism and German Romanticism. Manifestations of Szymanowski's Polish musical heritage and his cultural and social isolation during the years of the First World War (1914-1918) are also found in this sonata.This study also provides a detailed analysis of Piano Sonata No.3 in terms of form, motivic unity, thematic development, harmony, and texture. Another important aspect of my study is the extensive use of musical examples drawn from the works of Debussy, Ravel, Wagner and Strauss to demonstrate the musical influences of both French Impressionism and German Romanticism in his third sonata. In this sonata, Szymanowski mirrors French Impressionistic sound and texture through the common use of whole-tone and pentatonic scales as well as unresolved harmonies, trills, 4ths and 9ths. While drawing upon these particular techniques of Debussy and Ravel, Szymanowski's third sonata retains strong German roots in the use of motivic unity, chromaticism and textural crescendi such as those found in the operas of Wagner and Strauss.