The sonata-allegro form is most often the opening movement of multi-movement Classical piece, such as a concerto or symphony. The sonata-allegro form consists of three main parts: the exposition, the development, and the recapitulation. Sometimes, an introduction precedes the exposition or a coda follows the recapitulation to conclude the form.

             If included, the introduction to the form is usually slower than the bulk of the movement, but it also introduces the movement's main key. The exposition presents the piece's primary theme, first in the main key and then, through transitions into secondary keys of the piece. The exposition of the sonata-allegro form also contains a closing sequence, or codetta. The codetta may derive from either the primary or the secondary key, or both.

             The second part of the sonata-allegro form develops the theme of the movement and sometimes challenges the themes entirely. The development section can be short or long, as the piece warrants, and can be generally, loose, unstructured, and free-form. Although the development will conclude with a return to the piece's basic theme and main key, the bulk of the section is varied in tone, theme, rhythm, and structure. The development will include instances of transposition, transformation, and other ways of shifting the overall feel of the piece before it enters the final phases.

             The sonata-allegro form concludes with a recapitulation, which is a reiteration of the exposition. However, whereas the exposition changes keys as well as theme, the recapitulation usually remains in the one main key even when it explores secondary themes. The transition and codetta are presented in the piece's primary key. A coda might follow the exposition.

             The sonata-allegro form is still being used in the composition of classical pieces. The form is considered dramatic and rewarding because it is both structured and flexible. As the opening sequence to a multi-movement classical piece, the sonata-allegro form serves as a lively and informative introduction to a concerto or symphony.