The Khazars (/ˈxɑːzɑːrz/) were a semi-nomadic Turkic people who established a major commercial empire in the late 6th century CE spanning modern southeastern Russia, southern Ukraine, and western Kazakhstan. It was the most powerful polity to emerge from the break-up of the Western Turkic Khaganate. Astride a major artery of commerce between Eastern Europe and Southwestern Asia, Khazaria became one of the foremost trading empires of the early medieval world, commanding the western marches of the Silk Road and playing a key commercial role as a crossroad between China, the Middle East, and Kievan Rus'. For some three centuries (c. 650–965), the Khazars dominated the vast area extending from the Volga-Don steppes to the eastern Crimea and the northern Caucasus.

For most of its history, Khazaria served as a buffer state between the Byzantine Empire, the nomads of the northern steppes, and the Umayyad and Abbasid Caliphates, having previously been Byzantium's proxy against the rival Sasanian Empire. Around 900, the Byzantines began encouraging the Alans to attack Khazaria; this move aimed to weaken Khazar control over Crimea and the Caucasus and facilitate imperial diplomacy and proselytizing towards the powerful Kievan Rus' in the north. By 969, Sviatoslav I of Kiev, the ruler of Kievan Rus', along with his allies, conquered the Khazar capital of Atil, ushering the decline and disintegration of Khazaria by the mid 11th century.

Although they were likely a confederation of different Turkic-speaking peoples, the precise origins and nature of the Khazars are uncertain, since there is no surviving record in the Khazar language and the state was multilingual and polyethnic. Their native religion is thought to have been Tengrism, like that of the North Caucasian Huns and other Turkic peoples, although their multiethnic population seems to have included pagans, Jews, Christians, and Muslims. Although there is evidence that the ruling elite of the Khazars had converted to Rabbinic Judaism in the 8th century, the scope of the conversion to Judaism within the khanate remains uncertain.

The Khazars are variably believed to have contributed to the ethnogenesis of numerous peoples, including the Hazaras, Hungarians, Kazakhs, the Don and Zaporozhian Cossacks, Kumyks, Krymchaks, Crimean Karaites, Csángós, Mountain Jews, and Subbotniks. The late 19th century saw the emergence of a theory that the core of today's Ashkenazi Jews are descended from a hypothetical Khazarian Jewish diaspora that migrated westward into modern France and Germany. Linguistic and genetic studies have not supported the theory, and despite occasional support, most scholars view it with considerable scepticism. The theory is sometimes associated with antisemitism.

In Oghuz Turkic languages, the Caspian Sea is still named the "Khazar Sea", reflecting the enduring legacy of the medieval Khazar state.

Gyula Németh, following Zoltán Gombocz, derived Khazar from a hypothetical *Qasar reflecting a Turkic root qaz- ("to ramble, to roam") being an hypothetical retracted variant of Common Turkic kez-; however, András Róna-Tas objected that *qaz- is a ghost word. In the fragmentary Tes and Terkhin inscriptions of the Uyğur empire (744–840) the form Qasar is attested, although uncertainty remains whether this represents a personal or tribal name, gradually other hypotheses emerged. Louis Bazin derived it from Turkic qas- ("tyrannize, oppress, terrorize") on the basis of its phonetic similarity to the Uyğur tribal name, Qasar. Róna-Tas connects qasar with Kesar, the Pahlavi transcription of the Roman title Caesar.

D. M. Dunlop tried to link the Chinese term for "Khazars" to one of the tribal names of the Uyğur, or Toquz Oğuz, namely the Qasar (Ch. 葛薩 Gésà). The objections are that Uyğur 葛薩 Gésà/Qasar was not a tribal name but rather the surname of the chief of the 思结 Sijie tribe (Sogdian: Sikari) of the Toquz Oğuz (Ch. 九姓 jĭu xìng), and that in Middle Chinese the ethnonym "Khazars" was always prefaced with Tūjué, then still reserved for Göktürks and their splinter groups, (Tūjué Kěsà bù:突厥可薩部; Tūjué Hésà:突厥曷薩) and "Khazar's" first syllable is transcribed with different characters (可 and 曷) than 葛, which is used to render the syllable Qa- in the Uyğur word Qasar. While it is far from given that the Khazars are not signifying a multi-ethnic and multi-lingual cluster of peoples and clans, some more nomadic, some less, it doesn't exclude that some clans, or splintergroups, or even rulers has identified with the name(s) of the Khazars, in the variety of ways it has been expressed.

After their conversion it is reported that they adopted the Hebrew script, and it is likely that, although speaking a Turkic language, the Khazar chancellery under Judaism probably corresponded in Hebrew.