Fernando Sor (baptised 14 February 1778 – 10 July 1839) was a Spanish classical guitarist and composer of the early Romantic era. Best known for writing solo classical guitar music, he also composed an opera (at the age of 19), three symphonies, guitar duos, piano music, songs, a Mass, and at least two successful ballets: Cinderella, which received over one hundred performances, and Hercule et Omphale.

Partly because Sor was himself such a classical guitar virtuoso—contemporaries considered him to be the best in the world—he made a point of writing didactic music for players of that instrument of all levels. His Twelve Studies Op. 6, the Twelve Studies Op. 29, the (24) Progressive Lessons Op. 31, and the (24) Very Easy Exercises Op. 35 have been widely played for two hundred years and are regularly reprinted. On the other hand, some of Sor's music, not least his popular Introduction and Variations on Mozart's "Das klinget so herrlich" Op. 9, is fiendishly difficult.

Unlike modern classical guitar players, Sor used the smaller, slimmer "Romantic" guitars predating today's familiar Torres instrument. He used the ring finger of his plucking hand "rarely" and "only for harmony (never for melody)." He eschewed the use of nails on that hand.