Variations on a Theme of Paganini

Variations on a Theme of Paganini, Op. 35, is a work for piano composed in 1863 by Johannes Brahms, based on the Caprice No. 24 in A minor by Niccolò Paganini.
Brahms intended the work to be more than simply a set of theme and variations; each variation also has the characteristic of a study. He published it as Studies for Pianoforte: Variations on a Theme of Paganini. The work was dedicated to the piano virtuoso Carl Tausig.
It is well known for its emotional depth and technical challenges. David Dubal describes it as "a legend in the piano literature," and "fiendish," "one of the most subtly difficult works in the literature." Clara Schumann called it "Hexenvariationen" (Witch's Variations) because of its difficulty. Dubal quotes critic James Huneker:
“Brahms and Paganini! Was ever so strange a couple in harness? Caliban and Ariel, Jove and Puck. The stolid German, the vibratile Italian! Yet fantasy wins, even if brewed in a homely Teutonic kettle ... These diabolical variations, the last word in the technical literature of the piano, are also vast spiritual problems. To play them requires fingers of steel, a heart of burning lava and the courage of a lion.”
The work consists of two books. Each book opens with the theme, Paganini's Caprice No. 24 in A minor, followed by fourteen variations. The final variation in each section is virtuosic and climactic.