rabbi and Talmudic scholar primarily known for his lengthy quarrel with Rabbi Jonathan Eybeschütz (Eybeschütz, Jonathan) (q.v.), an antagonism that sundered European Jewry.

Emden was thoroughly trained as a scholar of the Talmud, the rabbinical compendium of law, lore, and commentary. Emden evinced more widespread interests as well, studying Latin and Dutch. His traditionalism was revealed, however, in his belief that a Jew should pursue such secular subjects only during the twilight hour. Emden was a rabbi, serving four years in the city from which he took his name.

After moving to Altona, he established his own private synagogue and printing press and revealed a cantankerous nature in the frequent disputes he engaged in with members of the Jewish community. He attacked such people as the chief rabbi of the community, Ezekiel Katzenellenbogen, for his Talmudic decisions. When Katzenellenbogen died, Jonathan Eybeschütz (Eybeschütz, Jonathan), a rabbi of great popularity and European reputation, was chosen to take his place. Eybeschütz prescribed amulets to save women from death in childbirth, and one of the charms, with a prayer in cipher to Shabbetai Tzevi, the most important of the Jewish false messiahs, fell into Emden's hands. He publicly denounced the maker of the amulet (without specifying Eybeschütz) as a heretic deserving excommunication, thereby initiating a long, often violent quarrel.

Emden was a prolific and distinguished author of polemical writings, in which he attacked Shabbetaian heresies, and of religious commentaries. His diary is revealing as a record of Jewish thought in his time, and his critical study of the Zohar (Sefer ha-zohar), part of the Jewish mystical writings known as the Kabbala, made clear that it was the work of several hands.