Nikolay Diletsky (Ukrainian: Микола Дилецький, Mykola Dyletsky, Russian: Николай Павлович Дилецкий, Nikolay Pavlovich Diletsky, Nikolai Diletskii, Polish: Mikołaj Dilecki, also Mikolaj Dylecki, Nikolai Dilezki, etc.; c. 1630, Kiev – after 1680, Moscow) was a theorist and composer of Ukrainian nationality, active in Russia. He was widely influential in late 17th-century Russia with his treatise on composition, A Musical Grammar, of which the earliest surviving version dates from 1677. Diletsky's followers included Vasily Titov.
Little is known about Diletsky's life. A remark by Ioannikii Trofimovich Korenev, a fellow theorist who describes him as a resident of Kiev, is considered evidence of Diletsky's Ukrainian origins. Korenev's statement is probably reliable, as he and Diletsky apparently were well acquainted. However, the date and even the year of birth are not known, and no details on Diletsky's early life have surfaced. He must have moved to Vilnius before 1675, because that year his Toga zlota ("The golden toga") was published there. The text is now lost, but it is known that it was written in Polish, and the surviving title page indicates that it was probably a panegyrical pamphlet. Some sources indicate that he wrote at least one other musical treatise while in Vilnius, which is now lost: this treatise is first mentioned in Grammatika musikiyskago peniya (1677), and the Idea grammatikii musikiiskoi (1679) is described as a translation of the Vilnius work in its title page.
After Vilnius, Diletsky lived in Smolensk, where in 1677 the first surviving version of his magnum opus, Grammatika musikiyskago peniya ("A grammar of musical song"), was written. He then moved to Moscow, where the subsequent two versions of the work appeared in 1679 and 1681. Nothing further is known about Diletsky's life, and it is generally assumed that he died shortly afterwards. His date of birth is projected from this hypothesis.