Khalaj is a Turkic language spoken in Iran. Although it contains many old Turkic elements, it has become widely Persianized. Khalaj has about 150 words of uncertain origin.

Surveys have found that most young Khalaj parents do not pass the language on to their children; only 5% of families teach their children the language.

The Khalaj language is a descendant of an old Turkic language called Arghu. The 11th-century Turkic lexicographer Mahmud al-Kashgari was the first person to give written examples of the Khalaj language, which are mostly interchangeable with modern Khalaj.

Gerhard Doerfer, who first scientifically described Khalaj, demonstrated that it was an independent branch from Common Turkic.

The Turkic languages are a language family of at least 35 documented languages spoken by the Turkic peoples.

While initially thought to be closely related to Azerbaijani, linguistic studies, particularly those done by Gerhard Doerfer, led to the reclassification of Khalaj as a distinct non-Oghuz branch of the Turkic language family. Evidence for the reassignment includes the preservation of the vowel length contrasts found in Proto-Turkic (PT), word-initial *h, and the lack of the sound change *d > y characteristic of Oghuz languages.

The conservative character of Khalaj can be seen by comparing the same words across different Turkic varieties. For example, in Khalaj, the word for 'foot' is hadaq, while the cognate word in nearby Oghuz languages is ayaq (compare Turkish ayak). Because of the preservation of these archaic features, some scholars have speculated that the Khalaj people are the descendants of the Arghu Turks.

Ethnologue and ISO formerly listed a Northwestern Iranian language named "Khalaj" with the same population figure as the Turkic language. The Khalaj speak their Turkic language and Persian, and the supposed Iranian language of the Khalaj is spurious.