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.

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.

The village is famous for the Battle of Kleidion of 29 July 1014, in which Tsar Samuil's forces were routed by Byzantine Emperor Basil II's army.

Klyuch is also famous for several alleged cases of UFO, mostly popularized by the local Kiril Yakimov.