Until now, no attempt has been made in English and American publications to double-check and clarify the reading of the main Hebrew manuscript containing information regarding the Khazars, nor to make a scientific translation of it into English. Moreover, the first of the texts discussed in this work has not been published before. Discovered in 1962 among the fragments of the Cairo Geniza held in the Cambridge University Library, it is in some respects the most valuable medieval text relating to the history of the Khazars. Unlike other Jewish manuscripts and other known medieval sources containing information about this people, this manuscript is an autograph, a genuine document - and not a later copy - and clearly written by Khazar Jews who lived in Kyiv in the first half of the 10th century.