Popularly known as Moonlight Sonata, Ludwig van Beethoven's Piano Sonata No. 14 in C-sharp minor was initially given the entitled "Quasi una fantasia" by Beethoven, meaning "almost a fantasy." The title "Moonlight Sonata" was derived from remarks made by music critic Ludwig Rellstab after Beethoven's death.

Written in 1801 and dedicated to his pupil Giulietta Guicciardi, Moonlight Sonata remains one of the most popular classical music works to this day. The first movement, in particular, is the recognizable by the triplets running through it.