In 1819 the publisher and composer Anton Diabelli invited 50 Austrian composers to write one variation a short waltz he had composed. He specified that it take up just one sheet (which he supplied) and this already contained his waltz. Composers such as Czerny, Moscheles, Hummel, Kalkbrenner, Liszt (just 10 years old), Schubert and Beethoven were among those invited. All except one provided their contribution. That one was Beethoven, who, electrified by Diabelli’s Waltz produced a massive work comprising 33 variations which was completed after the composer had completed the Missa Solemnis, and the last three piano sonatas. He delivered it to Diabelli in 1823, making it his final masterpiece. This huge work is one of the peaks of the repertoire for solo piano, it still baffles the listener, it still has the capacity to reveal more than we thought we knew about it. It makes extreme demands upon the performer and the listener, and in a great performance never ceases to surprise and shock the listener.