This book introduces a new theory of form for the analysis of instrumental music of the classical style that focuses on formal function--how the music works and where it is going. Building upon ideas first advanced by Arnold Schoenberg and later developed by Erwin Ratz, the theory provides a broad set of principles and a comprehensive methodology for the analysis of classical form, ranging from the individual ideas making up various phrases of themes to the large-scale organization of complete movements. The book includes a detailed discussion of standard theme types, considers more extensive formal regions, and finally treats the basic organization of the full-movement form. The theoretical concepts are illustrated with over 250 annotated musical examples from Haydn, Mozart, and Beethoven.