The Khazars (Old Turkic: ) were semi-nomadic Turkic people who established one of the largest polities of medieval Eurasia, with the capital of Atil and territory comprising much of modern-day European Russia, western Kazakhstan, eastern Ukraine, Azerbaijan, large portions of the northern Caucasus (Circassia, Dagestan), parts of Georgia, the Crimea, and northeastern Turkey. Khazar inscriptions are mainly in an eastern Turkish runic script. Khazar Correspondence is one of the very few primary sources on history of Khazars.

A successor state of the Western Turks, Khazar Khaganate (simply Khazaria) was a polyethnic-multifaith state with a population of Turkic, Uralic, Slavic, and Caucasian peoples. Khazaria was the first feudal state to be established in Eastern Europe. Khazaria was one of the major arteries of commerce between northern Europe and southwestern Asia, as well as a connection to the Silk Road. The name "Khazar" is found in numerous languages and seems to be tied to a Turkic verb form meaning "wandering" (Modern Turkish: Gezer). Because of their jurisdiction over the area in the past, Turkic people today still call the Caspian Sea the Khazar Sea. Pax Khazarica is a term used by historians to refer to the period during which the Khazaria dominated the Pontic steppe and the Caucasus Mountains.

The period when the Khazars had their greatest power corresponded with the European Dark Ages, and took place at a very important time for the creation of capitalism. Its strategic importance between China on one side and the Middle East and Europe on the other, temporarily gave all of Eurasia incredible riches.

In medieval (9th-11th centuries) Byzantine sources written in Greek, Khazaria was referred to as Eastern Tourkia (Τουρκία), whereas the Principality of Hungary was referred to as Western Tourkia.

Khazaria had an ongoing entente with Byzantium. Serving their partner in wars against the Abbasid Caliphate, Khazars aided the Byzantine emperor Heraclius (reigned 610–641) by sending an army of 40,000 soldiers in their campaign against the Persians in the Byzantine–Sassanid War of 602–628. In 775, Leo (son of Tzitzak) was crowned as the sole emperor of the Byzantine Empire. Sarkel (a Turkish word meaning White Fortress) was built in 830s by a joint team of Greek and Khazar architects to protect the north-western border of the Khazar state. The chief engineer during the construction of Sarkel was Petronas Kamateros (Πετρωνᾶς Καματηρός) who later became the governor of Cherson.

Khazars played a role in the balance of powers and destiny of world civilization. After Kubrat's Great Bulgaria was destroyed by the Khazars, some of the Bulgars fled to the west and founded a new Bulgar state (present day Bulgaria) near the Danubian Plain, under the command of Khan Asparukh. The most of the rest of the Bulgars fled to the north of the Volga River region and founded another state there called Volga Bulgaria (present day Chuvashia). The eldest son of Kubrat, Bat-Bayan Bezmer allied his Kara-Bulgars (Black Bulgars) with the Khazars. Kara-Bulgars were descendent of the tribes from Attila's state called Kutrigurs.

By serving as a buffer state between Christians and Muslims, the Khazars helped to block the western spread of Islam in Europe. Some scholars go to the extreme of arguing that, in the unlikely scenario Arabs had occupied what is now Ukraine and Russia, the Rus might never have been able to push south and east from the Baltic to establish Russia.

The Khazars had, for years, been venturing forth southward, in their marauding raids on the Muslim countries south of the Caucasus.

In a hadith, Khazars are mentioned as follows: Allah's Apostle (Mohammed) said, "The Hour will not be established until you fight with the Turks; people with small eyes, red faces, and flat noses. Their faces will look like shields coated with leather. The Hour will not be established till you fight with people whose shoes are made of hair." (Volume 4, Book 52, Number 179)

The major attempt of the Muslim armies to take control of the Transcaucasus came in 622 while Mohammed was still leading Islam. Islamic armies conquered part of Persia, Syria, Mesopotamia, Egypt, Armenia, and what is now the modern-day post-Soviet Republic of Azerbaijan and surrounded the Byzantine heartland (present-day Turkey) in a pincer movement which extended from the Mediterranean to the Caucasus and the southern shores of the Caspian. This was the time when the long series of wars called the Arab–Khazar Wars began. These wars largely ended with Arab defeats, with a fairly well-known commander, Abd ar-Rahman ibn Rabiah, perishing in one instance. The Arab armies' inability to traverse the Caucasus played a role in preventing them from succeeding in their siege of the Byzantine capital, Constantinople. Coupled with the military barrier presented by the Khazars themselves, this protected Europe from more direct and intensive assaults by the forces of Islam.

After fighting the Arabs to a standstill in the North Caucasus, Khazars became increasingly interested in replacing their Tengriism with a state religion that would give them equal religious standing with their Abrahamic neighbors. During the 8th century, the Khazar royalty and much of the aristocracy converted to a form of Judaism. Yitzhak ha-Sangari is the name of the rabbi who converted the Khazars to Judaism according to Jewish sources.

Khazars were judged according to Tōra (orders of the Khagan; coming from the root Tōr meaning customs; unwritten law of people in Old Turkic) (Modern Turkish: Töre), while the other tribes were judged according to their own laws.

Being a surprisingly tolerant and pluralistic society, even its army incorporated Jews, Christians, Muslims and Pagans at a time when religious warfare was the order of the day around the Mediterranean and in Western Europe. By welcoming educated and worldly Jews from both Christian Europe and the Islamic Middle East, Khazars rapidly absorbed many of the arts and technologies of civilization. As a direct result of this cultural infusion, they became one of the very few Asian steppe tribal societies that successfully made the transition from nomad to urbanite. Settling in their newly created towns and cities between the Caspian Sea and the Crimean Peninsula on the Black Sea, they became literate and multi-lingual agriculturalists, manufacturers and international traders.

Between 965 and 969, Khazar sovereignty was broken by Kievan Rus. Sviatoslav I of Kiev defeated them in 965 by conquering the Khazar fortress of Sarkel. Two years later, Sviatoslav conquered Atil, after which he campaigned in the Balkans. Medieval Ruthenian epic poems mention Ruthenian warriors fighting the Jewish Giant (Богатырь Жидовин). The Rus and the Hungarians both adopted the dual-kingship system of the Khazars (The kingship is divided between the khagan and the Bek. The Khagan was purely a spiritual ruler or figurehead with limited powers, while the Bek was responsible for administration and military affairs). The Rus princes even borrowed Turkic words like Khagan and Bogatyr. Many artifacts from the Khazars, exhibiting their artistic and industrial talents, have survived to the present day.

Read more about Khazars:  Origins and Prehistory, Language, Tribes, Extent of Influence, Decline and Fall, Khazars Outside Khazaria, Late References To The Khazars, Khazar Place Names Today, In Literature