The Khazar hypothesis of Ashkenazi ancestry, often called the Khazar myth by its critics, is a largely abandoned historical hypothesis that postulated that Ashkenazi Jews were primarily, or to a large extent, descended from converts to Judaism among the Khazars, a multi-ethnic conglomerate of mostly Turkic peoples who formed a semi-nomadic khanate in and around the northern and central Caucasus and the Pontic–Caspian steppe in the late 6th century CE. It is still sometimes used in antisemitic conspiracy theories and in various anti-Zionist approaches. The hypothesis draws on medieval sources such as the Khazar Correspondence, according to which at some point in the 8th–9th centuries, a small number of Khazars were said by Judah Halevi and Abraham ibn Daud to have converted to Rabbinic Judaism. The hypothesis also postulates that after collapse of the Khazar empire, the Khazars fled to Eastern Europe and made up a large part of the Jews there. The scope of the conversion within the Khazar Khanate remains uncertain, but the evidence used to tie the subsequent Ashkenazi communities to the Khazars is meager and subject to conflicting interpretations.
Speculation that Europe's Jewish population originated among the Khazars has persisted for two centuries, from at least as early as 1808. In the late 19th century, Ernest Renan and other scholars speculated that the Ashkenazi Jews of Europe originated among refugees who had migrated from the collapsed Khazarian Khanate westward into Europe. Though intermittently evoked by several scholars since that time, the Khazar-Ashkenazi hypothesis came to the attention of a much wider public with the publication of Arthur Koestler's The Thirteenth Tribe in 1976. It has been revived recently by geneticist Eran Elhaik, who in 2013 conducted a study aiming to vindicate it.
