In music, the term "variation" describes both a technique and a form. The technique of variation, the alteration of a musical idea, pervades every form, style and period of music from Gregorian chant to Serialism. Variation is fundamental. When this fundamental technique becomes the overriding principle that lends structure to a musical composition, variation is elevated from technique to form. If variation technique is the process, then variation form is the result. Accordingly, variation form derives from continuous and systematic variation technique. Variation form is governed by the idea of retention and alteration. With each variation, a composer chooses to retain some elements of the theme while altering others.

In doing so, he realizes that each variation promises new combinations of constants and changes. The balancing of innovation and continuity and its limitless possibilities account for the form's universal appeal. This dissertation explores the numerous methods that composers have adopted to mold the Variation form according to their own musical style and historical reference. The repertoire discussed and recorded focuses on independent strophic variation sets written for the keyboard. A survey of this repertoire produces the following categorizations: Harmonic Variations (basso ostinato and constant-harmony), Melodic Variations (constant-melody and melodic-outline), Character Variations (formal-outline and fantasy/free), Serial Variations, and Hybrid Variations. Certain variation types, namely constant-melody, serial, and fantasy/free, are synonymous with a particular time and repertoire because they wholly identifY with the aesthetics of a given historical period or style. Constant-harmony, melodic-outline, formal-outline and hybrid types are more pliable and thus produce a more diverse repertoire from multiple historical periods. The remaining form, basso ostinato, engenders a keyboard variation repertoire that spans six centuries; it is truly a universal form. While these conclusions are legitimate, they do not accurately convey the diversity of the variation repertoire. In the end, composers of all periods make individual choices in selecting which form or combination of forms best expresses their creative impulse.