Beethoven wrote 21 sets of variations for piano, but gave opus numbers to only 4 of them. The majority of the sets of variations were written on melodies from operas written by contemporary composers. The 32 Variations On An Original Theme does not have an opus number. It carries a WoO 80, number which is an abbreviation for 'without opus'. Why Beethoven never gave the work an opus number is anyone's guess. He only gave opus numbers to compositions he deemed worthy of being in his official catalog of compositions. Perhaps the piece didn't meet his standards, but the work was published in his lifetime, and has been popular with pianists and audiences ever since.
The work begins with the theme, an eight-bar, simple melody over a descending bass:
The variations are different in character, mood, and difficulty of execution. This is a work for an accomplished pianist with a good range of technique. The 32nd variation has some especially interesting rhythmic variation going on:
The right hand plays twenty-one notes to the measure while the left hand alternates between eight notes to the measure and ten notes to the measure. These compound rhythms gives the impression of an improvisation, and lead to what some consider a 33rd variation in paired sixteenth note slurs that are played off the beat. A short coda finishes the work, which averages about eleven minutes to play. Beethoven packs a lot of imagination and artistry in those few minutes, so much that the work can seem longer than it really is.