The Piano Sonata No. 14 in C-sharp minor, marked Quasi una fantasia, Op. 27, No. 2, is a piano sonata by Ludwig van Beethoven, completed in 1801 and dedicated in 1802 to his pupil Countess Julie “Giulietta” Guicciardi. Although known throughout the world as the Moonlight Sonata, it was not Beethoven who named it so. The name grew popular later, likely long after Beethoven’s death.

The piece is one of Beethoven’s most famous compositions for the piano, and was quite popular even in his own day. Beethoven wrote the Moonlight Sonata around the age of 30, after he had finished with some commissioned work; there is no evidence that he was commissioned to write this sonata.

Beethoven’s Piano Sonata No. 23 in F minor, Op. 57 (colloquially known as the Appassionata, meaning “passionate” in Italian) is among the three famous 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.

One of his greatest and most technically challenging piano sonatas, the Appassionata was considered by Beethoven to be his most tempestuous piano sonata until the twenty-ninth piano sonata (known as the Hammerklavier). 1803 was the year Beethoven came to grips with the irreversibility of his progressively deteriorating hearing.