Theme and variations usually a self-contained theme or song, either original or borrowed, followed by a series of self-contained variations, which generally preserve the phrase structure and length of the theme.

Variations often involve:
a. ornamentation of theme
b. change of texture, dynamics, mood, meter, tempo, or even mode
c. elaboration on harmonic pattern

Ground bass- a repeated bass-pattern with continuous variations overlayed. Sometimes the term passacaglia is used to describe this

Chaconne- continuous variations on a short theme or chord pattern

Great variation examples

Bach: "Crucifixus" from Mass in B minor (ground bass)
Bach: Goldberg Variations (aria with variations, many of them canonic)
Bach: "Chaconne" from Partita #2 in d minor for solo violin (based on a chord pattern)
Beethoven: Diabelli Variations (31 variations on a simple waltz)
Beethoven: Symphony #3, 4th movement (same themes also used in two other Beethoven works)
Beethoven: Symphony #7, 2nd movement (like Symphony #3, some aspects of sonata form blended in)
Beethoven: Symphony #9, 3rd and 4th movements (3rd movement uses two themes, 4th movement is based on "Song of Joy")
Schubert: "Trout" Quintet, 4th movement (theme is one of the composer's songs)
Brahms: Variations on a Theme of Haydn (a number of variations followed by a finale over a ground bass)
Brahms: Symphony #4, 4th movement (called passacaglia)
Elgar: Enigma Variations (based on an original theme; each character variation depicts a friend or relative of Elgar)
Rachmaninov: Rhapsody on a Theme of Paganini (for piano and orchestra)
Respighi: Ancient Airs and Dances Suite #2, Bergamasca