This dissertation has four principal goals:

1. to provide Heinrich Schenker's theoretical notion of improvisation with an historical context, thus laying the groundwork for a Schenkerian study of Chopin's 'improvisatory' compositions;
2. by analysing most of his early pieces and several mature ones, to define Chopin's 'structural style', i.e" the shared structural principles on which music from different genres was based; and by studying the evolution of his 'structural style' from 1817 to 1832, to show how Chopin developed the ability to conceive works as unified compositional statements rather than as a succession of independent sections;
3. to fill the gaps resulting from cursory treatment of Chopin's early and late music in the Schenkerian literature and in the work of other analysts;
4. to apply Schenkerian analytical techniques systematically to a wide body of repertoire in order to demonstrate the method's value as a musicological tool in defining the styles of other composers.

The influence that improvisation had on Chopin's music has often been noted, but discussion has generally been confined to foreground details without regard to tonal structure, This study of Chopin's 'improvisatory' works - stile brillante repertoire, early dance pieces, F minor Fantasy and Polonaise-Fantasy - reveals that improvisatory practices were also important in the evolution of his 'structural style'. Contrary to Schenker's assumptions about 'genius', Chopin only gradually developed the 'improvisatory long-range vision' - that is, the ability to conceive works in a unifying 'sweep of improvisation' - that characterises his later music. Many early pieces seem to have been 'formally' conceived, with self-contained parts juxtaposed to create the whole. As he matured as a composer, Chopin learned to relate independent sections by means of structural voice-leading, tonal architecture, and an increasingly organic use of motivic and harmonic material.

Overview of selected middle- and late-period works and detailed analysis of the Barcarolle and Polonaise-Fantasy show that structural principles established in Chopin's 'apprenticeship' remained a central feature of his mature 'structural style' despite the music's greater sophistication at the foreground level and the stylistic changes that occurred in the early 1840s. Chopin's reliance on these principles is particularly noteworthy in the Polonaise-Fantasy, which in the foreground conveys a sense of improvisatory freedom to the point of apparent disorder.