The Waldstein Sonata, officially known as Piano Sonata No. 21 in C major, Op. 53, is a significant work composed by Ludwig van Beethoven in 1804-1805. It is named after the patron Count Ferdinand Waldstein, who supported Beethoven during this period. The sonata is known for its innovative structure and emotional depth, showcasing Beethoven's transition from the Classical to the Romantic style. The sonata consists of three movements: the energetic Allegro con brio, the lyrical Introduzione (Adagio molto semplice e cantabile), and the spirited Rondo (Allegro).