The Pre-Greek substrate consists of the unknown pre-Indo-European language(s) spoken in prehistoric Greece before the advent of the Proto-Greek language in the Greek peninsula during the Bronze Age. It is possible that Greek acquired approximately 1,000 words from such a language or group of languages, because some of its vocabulary cannot be satisfactorily explained as deriving from Proto-Greek and a Proto-Indo-European reconstruction is almost certainly impossible for such terms.

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus, Italy, southern Albania, and other regions of the Balkans, the Black Sea coast, Asia Minor, and the Eastern Mediterranean. It has the longest documented history of any Indo-European language, spanning at least 3,400 years of written records. Its writing system is the Greek alphabet, which has been used for approximately 2,800 years; previously, Greek was recorded in writing systems such as Linear B and the Cypriot syllabary. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Coptic, Gothic, and many other writing systems.