Most of Bach's clavier works cannot be precisely dated, although various autograph manuscripts and prints sometimes supply dates for the completion of a collection; in certain cases, a work exists in several versions. Among the earlier works are toccatas, capriccios, fantasias, fugues, variations, suites, sonatas, and miscellaneous shorter pieces for teaching.
The most significant large-scale pieces completed by the time Bach left Cöthen (and in fact mostly written during the Cöthen period) are the toccatas in C minor and in F-sharp minor, the "English" and "French" Suites, and the Well-Tempered Clavier, Book I (dated 1722). The toccatas are multi-sectional works, each mixing free improvisatory-like sections with fugues. The suites are a blending of German, Italian, and French approaches (e.g., Bach uses both the French and Italian types of courantes); in comparison with the so-called "French" Suites, the "English" Suites are generally more expansive, each beginning with a Prelude. Bach's Well-Tempered Clavier, Book I, is a masterful collection of twenty-four preludes and fugues, in all the major and minor keys. The mono-thematic fugues, in two to five voices, present an amazing variety of techniques and structures.
Bach's clavier works from the Leipzig period include a second set of twenty-four preludes and fugues (Well-Tempered Clavier, Book II, although not so-named on the manuscript; completed around 1742), and the Clavier-Übung, Vols. I, II, and IV. Vol. I (1731, although published in installments in 1726-1731) contains six suites, called Partitas, in which sets of highly stylized dances are preceded by different kinds of introductory movements (variously entitled Praeludium, Praembulum, Sinfonia, Fantasia, Overture, and Toccata). Vol. II (1735) has two compositions, each modeled on a different orchestral genre: the Italian Concerto transfers the forms and styles of a Vivaldi-like concerto to harpsichord, while the Overture in French Style is an imitation of the typical orchestral suite popular in Germany during the late Baroque. Vol. IV (1741-1742), the so-called Goldberg Variations, has an aria (binary theme section in sarabande style) with thirty variations. Every third variation is a canon, with the interval of imitation progressing from a unison (first canon) to the ninth (last canon); other variations explore a wealth of keyboard figurations and forms (e.g., virtuoso two-art writing, fughetto, lament, French overture, etc.).