This book introduces a new theory of form for the analysis of instrumental music of the classical style. Focusing on formal function - the role a formal unit plays in the structural organization of a work - the theory provides a broad set of principles and a comprehensive methodology for the analysis of classical form - 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, more extensive formal regions, and full-movement forms. The theoretical concepts are illustrated by over 250 annotated musical examples by Haydn, Mozart and Beethoven.