The various institutions of Rabbeinu Gershom:
Rabbeinu Gershom was a famous leader of Ashkenazi Jewry throughout the early 11th century, making various institutions on Ashkenazi Jewry that have reverberating effects until this very day. Rabbeinu Gershom was born in the year 960 in France, but he later moved to Maintz, Germany, where he set up his school and leadership. His scholarship and leadership skills which held rabbinic authority over all the lands of Ashkenaz, earned him the title “Meor Hagoleh” which literally means “the light of the exile.” During his years of rule, he made various Takanos, or institutions, many of which we deal with civil law and marriages and were instituted for the sake of increasing in the establishment of peace between a husband and wife and amongst fellow Jews and their Gentile neighbors. Many of these institutions carried with them a Cherem, which is a severe penalty of excommunication if anyone transgresses them, hence becoming known “Cherem DeRabbeinu Gershom.” In total, we can trace 83 institutions to Rabbeinu Gershom, as listed by the various Poskim. His personality and leadership was so powerful that even centuries later Ashkenazi Jewry still considered themselves his students, and viewed his institutions as if they were handed by Moses on Sinai. He passed away in the year 1040, [although some historians say 1028], in Mainz, Germany.
The following is a short overview of some of his most major and famous institutions which are binding until this very day:
- A ban on polygamy-not to marry another wife in addition to one’s current wife.
- Consent for divorce-a ban against divorcing one’s wife without her consent.
- Intrusion of privacy-A ban against reading another person’s mail.
- Business ethics-Offering to outbid a potential renter of the house of a Gentile who is a ready in discussions with the owner.
- Not to nullify the Tamid [i.e. the Minyan in Shul] on Shabbos for the sake of resolving a civil dispute of private individuals.
The reason he was given the title of “Meor Hagoleh/the light of the exile”:
It is traditionally stated that the reason why Rabbeinu Gershom was given the title of “Meor Hagoleh/the light of the exile” is because two of his institutions carried with them major weight above in heaven in protecting the Jewish people as God’s chosen nation for eternity. Rabbeinu Gershom instituted that a man may not divorce his wife against her will and also may not marry another wife in addition to his first wife. Tradition states that the spiritual reason behind this institution is because Rabbeinu Gershom saw in the heavens that the angelic minister of Edom, which in those days was the Christian nation, was prosecuting a claim that the Jewish people have abandoned the faith and therefore God should rather choose the Christian nation in place of the Jewish people. Accordingly, Rabbeinu Gershom made an institution prohibiting a husband from divorcing his wife against her will, thus, so to say binding God to do the same and never divorce the Jewish people. However, the prosecution in heaven continued with saying that since the Jewish people are not faithful to the law, at the very least God should choose for himself an additional nation to the Jewish people, and therefore choose also the Christian nation. To combat this new heavenly prosecution, Rabbeinu Gershom instituted that a husband may not marry another wife in addition to his first wife, hence closing any further ability of God in heaven forbid divorcing his nation Israel or choosing another nation in addition to the Jewish people.
 See Encyclopedia Talmudit Vol. 17 p. 378 [Erech Cherem Rabbeinu Gershom]
 See Rashi on Yeshaya 46:1 and Beitza 24b
 See Encyclopedia Talmudit Vol. 17 for a list of all 83 institutions; Institutions 1- 38 are allocated from Orchos Chaim Vol. 3; Institution 39-82 are allocated from Shut Maharam Ben Baruch 1022. See also: Machzor Vitri 102; Beir Hagoleh Y.D. 334; Pachad Yitzchak Takanos Rabbeinu Gershom
 Rashi in Teshuvos Chachmei Tzarfat 21
 See Teshuvos HaRosh 43:8
 Shut Maharshal 29; Encyclopedia Talmudit ibid footnote 1
 Encyclopedia Talmudit ibid lists the first three as his most major institutions discussed in the Poskim
 Michaber E.H. 1:10
 Rama E.H. 119:6
 Shut Maharam Merothenberg 1022; Kol Bo 116; Maharam Mintz 102; Beir Hagoleh Y.D. 334; Kneses Hagedola 334:5; Halachos Ketanos 1:59;173; 276; Toras Chaim Maharchash 3:46; Chikikeiy Lev Y.D. 49; Beis David [Salonica] Y.D. 158; See Encyclopedia Talmudit Erech Cherem Rabbeinu Gershom
 Admur Hilchos Hefker and Hasagas Gevul Halacha 11; Rama C.M. 237:1; Maharam Padva 41
 Admur 339:3; Encyclopedia Talmudit ibid p. 767 Takana 16
 See Igros Kodesh 13:12 [Letter 4,283]; Sefer Keser Hayehudi, stories of Hayehudi Hakadosh of Peshischa; Sichos Chachamim of Rav Reuvein Margolis