Until recently, in rabbinic discourse as well as Israeli state policy, Jewish identity was not reckoned via genetics. While academic studies looked for genetic similarities among Jewish communities, these similarities did not determine Jewishness or state policy. This article is the first study spotlighting the novel use of mtDNA testing in order to determine the Jewishness of Israeli citizens who immigrated to Israel from the Former Soviet Union (FSU) 1990 onward. These tests offered by the Israeli State Rabbinate are accompanied by heated political and religious wrangles, in particular between leaders of the Ultra-Orthodox Jewish community and the political party claiming to represent immigrants from the FSU. We aim to understand this current debate on determining Jewishness by mtDNA. We examine the reciprocal relationship between science, religion, communal identity and state policy, and question the possible social implications. In contrast to claims that the change in Jewish’ definition is guided by science and technology, we argue that this change is dictated primarily by specific historical and socio-political circumstances. Furthermore, enthusiasm or rejection of the use of mtDNA for Jewish recognition depends on inclusive or exclusive ideologies, not on the indecisive content of science or religion themselves.