Yaakov ben Moshe Levi Moelin (Hebrew: יעקב בן משה מולין) (c. 1365[1] – September 14, 1427) was a Talmudist and posek (authority on Jewish law) best known for his codification of the customs (minhagim) of the German Jews.

It contains a detailed description of religious observances and rites, at home and in the synagogue, and thus provides an authoritative outline of the minhagim of the German Jews.

It had a great influence on the Jews of Central Europe and was largely responsible for the importance attached to minhag in these communities.

These were collected and edited by Rabbi Yitzhak Satz, and, published in 1977 under the title SHuT Maharil heChadashot ("New Responsa of Yaakov Molin").

[2] Recently, the German esoteric scholar Georg Dehn has argued that the MaHaRIL was also the author of The Book of Abramelin, which he wrote under the pseudonym of Abraham von Worms.

In his critical edition of Minhagei Maharil, Shlomo Shpitzer surveyed 22 manuscripts of the work and noted that "The only thing common between them was that no on text was like the other.