Most of us know that Jews today don't engage in Polygamy, and most of us also know that Jews used to engage in lots of Polygamy (about 40 men in the Torah had more than one wife). King David had eight wives and a bunch of concubines. Soloman had like, 700 wives!
But until far more recently (if you trust the Jewish Encyclopedia), Jews were okay with a man marrying multiple women (though not so much the other way around):
Permitted according to biblical law, polygamy was practiced throughout the talmudic period and thereafter until the tenth century (Piskei ha-Rosh to Yev. 65a; Sh. Ar., EH 1:9). Already in amoraic times, however, the practice was frowned upon by the sages, who prescribed that polygamy was permissible only if the husband was capable of properly fulfilling his marital duties toward each of his wives
Whoa! The tenth century?
Just wait… it gets better. According to Wikipedia, the Torah:
includes a few specific regulations on the practice of polygamy, such as Exodus 21:10, which states that multiple marriages are not to diminish the status of the first wife; Deuteronomy 21:15-17, which states that a man must award the inheritance due to a first-born son to the son who was actually born first, even if he hates that son's mother and likes another wife more; and Deuteronomy 17:17, which states that the king shall not have too many wives. One source of polygamy was the practice of levirate marriage, wherein a man was required to marry and support his deceased brother's widow.
In the modern day, Rabbinic Judaism has essentially outlawed polygamy. Ashkenazi Jews have followed Rabbenu Gershom's ban since the 11th century. Some Sephardi and Mizrahi Jews (particularly those from Yemen and Iran, where polygamy is a social norm) discontinued polygamy much more recently, as they emigrated to countries where it was forbidden. The State of Israel has forbidden polygamous marriages, but instituted provisions for existing polygamous families immigrating from countries where the practice was legal.
Now, the rest of this seems not-so-shocking. But that last line– I'll admit I'm a little surprised to discover that there are still Jewish polygamous families today. Sadly, I found sites online that use this information to build terribly anti-Semitic arguments about how Israel supports Polygamy as a practice, though I won't link them here.