The Piano Sonata No. 14 in C-sharp minor "Quasi una fantasia", Op. 27, No. 2, popularly known as the Moonlight Sonata, is a piano sonata by Ludwig van Beethoven. Completed in 1801 and dedicated in 1802 to his pupil, Countess Giulietta Guicciardi, it is one of Beethoven's most popular compositions for the piano.