Ludwig van Beethoven's Piano Sonata No. 23 in F minor, Op. 57 (colloquially known as the Appassionata) is a piano sonata. It is considered one of the three great piano sonatas of his middle period (the others being the Waldstein, Op. 53 and Les Adieux, Op. 81a). It was composed during 1804 and 1805, and perhaps 1806, and was dedicated to Count Franz von Brunswick. The first edition was published in February 1807 in Vienna.

Unlike the early Sonata No. 8, Pathétique, the Appassionata was not named during the composer's lifetime, but was so labeled in 1838 by the publisher of a four-hand arrangement of the work.

The Appassionata was considered by Beethoven to be his most tempestuous piano sonata until the twenty-ninth piano sonata known as the Hammerklavier being described as a "brilliantly executed display of emotion and music".^{[citation needed]} 1803 was the year Beethoven came to grips with the irreversibility of his progressively deteriorating deafness.

An average performance of the entire Appassionata sonata lasts about twenty-three minutes.