This lecture initiates a discussion of Classical-era instrumental musical form that will continue through Lecture Twenty-Five. In this lecture, we examine theme and variations form, which represented an adaptation of Baroque-era variations procedure to the expressive and musical needs of the Classical Era. While maintaining much of the compositional rigor of the Baroque models, Classical-era theme and variations form utilizes a “tune” as its theme rather than a bass line. Wolfgang Mozart’s Variations on “Ah, vous dirai-je, maman” is used as an example of Classical-era theme and variations form.