Klyuch (Bulgarian: Ключ, "key"; also transliterated Кључ, Ključ, Kliuch, Kljuch, etc., Medieval Greek: Κλειδίον, Kleidion, Latin: Clidium) is a village in south-westernmost Bulgaria, part of Petrich Municipality, Blagoevgrad Province. It lies 455 metres above sea level. As of 2005, it has a population of 1,113 and the mayor is Hristo Markov.
Klyuch lies at the northern foot of the Belasitsa mountains, south of the Strumeshnitsa River, in the geographic region of Podgorie. The climate is transitional Mediterranean, with a summer minimum and a winter maximum of precipitation.