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 student, Countess Giulietta Guicciardi, it is one of Beethoven's most popular musical compositions for the piano.