The article explores the history of the Judaizers’ heresy, situating it in the broader context of the religious tradition of medieval Rus’. The author maintains that the Judaizers movement was not just a Christian heresy fed by the anticipation of apocalypses, but also a fact of Judaic proselytism. In order to understand why such proselytism was possible in Rus’ and virtually impossible in other Christian countries, the author scrutinizes specific features of the Rus’ Christian tradition. He suggests the centrality of the Old Testament concepts and tropes for the medieval Russian religious tradition due to the specificity of the reception of Christianity, the relationship between Byzantium and Rus’, and the overlapping of confessional and political boundaries in the ancient Russian state. The impact of the Old Testament culture on Russian Orthodox Christianity and the closure of Russian culture in the XIV century laid the groundwork for the particular receptivity to the Judaic proselytism.