Girolamo Diruta (c. 1554 – after 1610) was an Italian organist, music theorist, and composer. He was famous as a teacher, for his treatise on counterpoint, and for his part in the development of keyboard technique, particularly on the organ. He was born in Deruta, near Perugia.
Little is known of his biography except for some details during his principal period of activity. He is known to have become a Franciscan in 1574, and to have gone to Venice in 1580, where he met Claudio Merulo, Gioseffo Zarlino and Costanzo Porta (who was also a Franciscan), and he probably studied with each of them. Merulo mentioned Diruta in a letter of recommendation, probably from the 1580s, as one of his finest students. By 1593 he was organist at Chioggia cathedral, and by 1609 he was organist at Gubbio. Nothing is known of him after 1610, when he dedicated his treatise Il transilvano to Sigismund Bathory, prince of Transylvania, and to Leonora Orsini Sforza, niece of Grand Duke Ferdinand I of Tuscany.
His nephew Agostino Diruta (c. 1595 – c. 1647) was also a composer, and his pupil.
Diruta's major work is a treatise in two parts on organ playing, counterpoint, and composition, entitled Il Transilvano (The Transylvanian) published for the first time in 1593; it is in the form of a dialog with Istvan de Josíka, a diplomat from Transylvania whom Diruta met during one of Josíka's missions to Italy. It is one of the first practical discussions of organ technique which differentiates organ technique from keyboard technique on other instruments. His fingerings largely follow the usual ones of his times: for example, his fingering for a C major scale never includes the thumb, and crosses the middle finger over the ring finger: his work is one of the earliest attempts in Italy to establish consistency in keyboard fingering.