During the Classical period, sonata form, or sonata allegro form, became the standard way to open the first movement of a sonata, symphony, string quartet, or concerto. This form typifies the Classical period because it is balanced and ordered and has logical harmonic progression. Even though this makes it sound formulaic and boring, the composer was able to add their own style to this standard form to make sure that each composition was different and said what they intended.

Sonata form is based on a ternary, or three-part, pattern featuring the Exposition, Development, and Recapitulation. The exposition opens the movement and is where the composer introduces the main theme or themes in the home key of the work. As the exposition proceeds, the composer will use the melody in a variety of ways, changing and manipulating it and eventually moving from the home key to a second harmonic center, in a section called the transition, normally from the tonic to the dominant, as discussed in the Theory section. Usually the new key features a contrasting melody that uses a different mood or rhythm than the first melody. The exposition ends with a cadence in the new key before returning to the beginning to repeat the entire section.

The development typically begins in the key that the exposition ended in, usually the dominant. As its name suggests, the development is where the composer can really explore the melodies they introduced during the exposition, altering and manipulating the individual themes and sometimes juxtaposing the two themes together. Through the section, different keys can be explored as well. Development sections vary widely in length; sometimes they are relatively short compared to the exposition, others are significantly longer. The music is typically more adventurous featuring interesting harmonies and rhythms. At the end of the development section, the composer will make their way back toward the tonic, the original home key of the work. This is called the retransition and helps signal that we are about to return to the original key and melody. Harmonically, composers often featured a prolonged dominant chord that resolves to the home key at the beginning of the final section, the recapitulation.

Sonata form ends with the recapitulation, an altered restatement of the exposition. The section starts with a restatement of the original music of the exposition in the same key and form as before. Unlike the exposition, however, the transition does not move to a new key, all the music stays in the home key during the recapitulation. The transition sometimes adds a new melody before the second melody returns, this time in the home key instead. The movement then makes it way towards a final cadence in the home key to end the form.

Composers used this basic structure of exposition, development, and recapitulation to organize their melodic and harmonic ideas. The sonata form was used not only for sonatas, but for the first movement of most instrumental music during the classical period. Although the same basic structure would be used, composers could add their own additions to make the form their own. Some composers would add an introduction before the exposition started in earnest. Often introductions would be slower than the rest of the work and would be based in the dominant key. Sometimes the themes from the introduction would occur later in the movement, sometimes not. Composers could also add a coda, literally tail in Italian, to the end of the work. If the composer includes a coda, it occurs after the final cadence of the recapitulation and usually contains music from the movement, no new melodies. Sometimes a coda can be very short, perhaps simply a series of extra chords to make sure we realize the movement has ended. Other works feature extended codas that are longer and more elaborate.

Although sonata form has a standard progression and expectation, each composer uses the form in their own way to express their musical ideas. Throughout the Classical period and beyond, composers have used sonata form. The range of ideas and ways that a standard form can be utilized helps to express the wide variety of creative genius within the world of music.