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The sonata form is a general way of organizing short pieces of music or individual movements of longer pieces. Although it first appeared in the classical era, it was not specifically described or named until the late nineteenth century. Mozart and Beethoven, the best known composers of sonatas, never heard of the term.
The sonata has at least three distinct sections. The first section, called the exposition, introduces the basic material of the piece. In the next section, the development, the material introduced in the exposition is fragmented, rearranged, and “discussed” in a dramatic way. Finally, the opening material returns in a more stable, confident form in a section called the recapitulation.
Later composers introduced variations on this form. Some sonatas have a brief introduction before the exposition. Some have a brief coda after the recapitulation. Since many sonata movements are in faster tempos, the introduction is usually slow, a stately preface to the body of the work. The coda generally stays in the main tempo, but sounds more conclusive. Early sonatas often repeated the exposition to establish basic themes before moving on to the development. Beethoven generally avoided this repetition, and most later composers followed his example.
The development section of the sonata is often divided into two parts, often called the “primary theme” and the “secondary theme” joined by a “bridge. ” These terms are useful in discussing some sonatas, but they do not apply to many examples of the form. Haydn, for example, typically used only one theme in the development section, and Beethoven sometimes used more than two. These terms are still helpful, though, in terms of describing key. The primary theme begins in the home key of the movement (also called the tonic) . The bridge provides a transition to a related key, called the dominant key or the relative major key if the tonic is a minor key. In other words, the fundamental purpose of the development' s two parts is not so much thematic as tonal.

The term “sonata” is commonly used to describe independent pieces of music, but the sonata form is also employed as the organizing principle of the movements in symphonies.