Jacob Ettlinger (17 March 1798 – 7 December 1871) (Hebrew: יעקב עטטלינגער) was an Ashkenazi rabbi and author, and one of the leaders of Orthodox Judaism. He is sometimes referred to as the Aruch la-Ner (ערוך לנר), after his best-known publication.

Ettlinger was born in Karlsruhe, Baden, and died in Altona, Prussia. He received his early education from his father Aaron, who was Klausrabbiner (rabbi of a small synagogue) in Karlsruhe. Aaron was also a recognized Talmudical scholar who was steeped in Kabbalah.

He then went to study under the Rabbi of Karlsruhe, Rabbi Asher Wallerstein, the son of the famed Shaagas Aryeh. Wallerstein was also the Chief Rabbi of the entire Grand Duchy of Baden. Ettlinger remained his student until the age of 18.

Ettlinger rounded off his Talmudical education in the yeshiva of Abraham Bing in Würzburg, one of the most significant Torah centers in Germany. While there, he attended the University of Würzburg, mainly studying philosophy. He was thus among the earliest German rabbis who possessed academic training. It should be pointed out, however, that he never received any formal degree.

The fact that Ettlinger stayed fervently Orthodox, even though he attended university, was considered by most to be an anomaly. Kaufmann Kohler reports that the saying was current that "Satan made him go through the university and come forth so immune and loyal, as to lure all the rest of [the] modern Rabbis to pursue those studies which caused their disloyalty to Modern Judaism".

In 1826 he was appointed Kreisrabbiner (district rabbi) of Ladenburg, with his seat in Mannheim, where he was at the same time chief prebendary (Klausprimator). This position he held until he succeeded Akiba Israel Wertheimer as Chief Rabbi of Altona, where he officiated from 1836 until his death. His ambit as Ashkenazi Chief Rabbi comprised Holstein and Schleswig and until 1864 also Denmark. In this position he became one of the most prominent representatives of German Orthodoxy.

His yeshiva was attended by a great many students preparing for the ministry, and many of them became leaders of Orthodoxy. Samson Raphael Hirsch was his disciple in Mannheim, and Azriel Hildesheimer in Altona. Five of his sons-in-law became prominent Orthodox rabbis: Joseph Isaacsohn of Rotterdam, Salomon Cohn [de] of Schwerin, Israel Meir Freimann of Ostrowo, Moses Löb Bamberger [de] of Kissingen and Markus Mordechai Horovitz of Frankfurt. He was the last German rabbi who acted as civil judge. Much against his will, the Danish government, to which Altona then belonged, abolished this right of the Altona Rabbi in 1863. The purity of his character and the sincerity of his religious views were acknowledged even by his opponents.

In his will, Ettlinger requested that he not be described as having been a "Tzaddik" (righteous individual), and that the inscription on his tombstone should contain merely the titles of his works and a statement of the number of years during which he was rabbi of Altona. He further asked that the four capital punishments (stoning, burning, decapitation and asphyxiation) be performed symbolically on his body.