Gershom ben Judah best known as Rabbeinu Gershom (in Hebrew: Our teacher Gershom) (c. 960 -1040? 1028?) and is also commonly known known by the longer title Rabbeinu Gershom Me'Or Hagolah (Our teacher Gershom the light of the exile) to scholars of Judaism. He was a famous Talmudist and Halakhist.

Rabbeinu Gershom was the head of a yeshiva in Mainz. He was the spiritual guide of the fledgling Ashkenazic Jewish communities and was very influental in molding them at a time when their population was dwindling. During his lifetime, some claim it was due to his greatness as a Talmudic scholar, Mainz became a center of Torah and Jewish scholarship for many Jewish communities in Europe that had formerly been connected with the Babylonian yeshivas. Students came from all over Europe to enroll in his yeshiva. His many students later dispersed among various communities in Germany and beyond which helped spread Jewish learning. Rashi of Troyes (d.1105) said less than a century after his death "all members of the Ashkenazi diaspora are students of his (i.e. Rabbeinu Gershom's) students".

Some have speculated that if Rabbeinu Gershom had never lived then there may not have been something known as "Ashkenazic Judaism" as it is known today. As early as the 14th century Asher ben Jehiel wrote that Rabbeinu Gershom's writtings were "such permanent fixtures that they may well have been handed down on Mount Sinai".

He is famous for his religious bans within Judaism, which include:

• The prohibition of polygamy.
• The prohibition of divorcing a woman against her will.
• The prohibition of reading private mail.

His bans are considered binding on all of Ashkenazic Jewry until the present day.