Messianic Judaism is a modernist and syncretic sect that considers itself Jewish. Many Jews and Jewish authority figures, both in the United States and Israel, consider it a part of Evangelical Christianity.

"Who is a Jew?" is a basic question about Jewish identity and considerations of Jewish self-identification. The question pertains to ideas about Jewish personhood, which have cultural, ethnic, religious, political, genealogical, and personal dimensions. Orthodox Judaism and Conservative Judaism follow Jewish law (Halakha), deeming people to be Jewish if their mothers are Jewish or if they underwent a halakhic conversion. Reform Judaism and Reconstructionist Judaism accept both matrilineal and patrilineal descent as well as conversion. Karaite Judaism predominantly follows patrilineal descent as well as conversion.