The 33 Variations on a waltz by Anton Diabelli, Op. 120, commonly known as the Diabelli Variations, is a set of variations for the piano written between 1819 and 1823 by Ludwig van Beethoven on a waltz composed by Anton Diabelli. It forms the first part of Diabelli's publication Vaterländischer Künstlerverein, the second part consisting of 50 variations by 50 other composers. It is often considered to be one of the greatest sets of variations for keyboard along with Bach's Goldberg Variations.

Ludwig van Beethoven was a German composer and pianist. He is one of the most revered figures in the history of Western music; his works rank among the most performed of the classical music repertoire and span the transition from the Classical period to the Romantic era in classical music. His early period, during which he forged his craft, is typically considered to have lasted until 1802. From 1802 to around 1812, his middle period showed an individual development from the styles of Joseph Haydn and Wolfgang Amadeus Mozart, and is sometimes characterized as heroic. During this time, Beethoven began to grow increasingly deaf. In his late period, from 1812 to 1827, he extended his innovations in musical form and expression.