For many centuries, "being a Jew" was equivalent to "performing the ceremonial laws of Judaism." Thus, ethnic and confessional principles coincided and reinforced the cultural identity of Jewry as an entity. Strong self-identification and in-group solidarity supported the high "ethnic temperature" of this group. The processes of secularisation, which first took place in modern Europe and then spread to other regions, led, therefore, to the "cooling" of the Jewish ethnic temperature. This process has its roots in different periods of Russian history and resulted in deep changes in Jewish identity.