Fact: Women participating in a meal in which there is a men’s zimun are obligated to participate. If there is no male zimun of ten and there are three or more women, they may form their own zimun. If there is no male zimun at all, many authorities obligate the women to form a zimun.
Background:  The Talmud records a tanaitic statement (Brachot 45b) that women form a zimun amongst themselves and it (Arachin 3a) includes women in the statement that “all are obligated in zimun.” In order to reconcile these statements with a seemingly contradictory one in Brachot (45a) that says that women may not have a zimun said over them, three approaches were adopted by the commentators. Tosafot views a woman’s participation in any zimun as optional. The Beit Yosef (author of the Shulchan
Aruch) and Shulchan Aruch Harav obligate women in zimun when a men’s zimun exists, but regard an independent women’s zimun as optional. The Rosh, Rokeach and Gra not only obligate women when a zimun of men exists but obligate three women who ate together to form a women’s zimun. Since the Shulchan Aruch requires women to participate in an existing men’s zimun, at a meal where there is a zimun of men, the obligation of zimun devolves on all present and the women are equally obligated to respond and may not bentch on their own later. Rav Shmuel Halevi Vozner (Shut Shevet Levi 1:OC:38) post facto defends the converse. He justifies men who leave to go to a rebbe’s table where they then bentch, thus leaving the women at home without a zimun. His justification is based on an otherwise rejected position of Rav Hai Gaon that it is the end of the meal that established the zimun obligation. This would not help in the case where all finish together and the women simply abstain from the zimun.
Women’s participation in zimun is thus already recorded in the Talmud. There is no halachic opinion that prohibits women from forming a zimun, and many opinions require it. In addition, if three or more women form a zimun there is no reason why one or two men who are present cannot remain and answer to this zimun. This is according to Rabbi Shlomo Zalman Auerbach as quoted by his nephew in Halichot Beisah. This opinion is also found in Toras HaYoledes by Rav Yitzchok Silberstein [son-in-law of
Rav Elyashiv] and Dr. Moshe Rothschild, 1987, translated by S. Ludmir, 1989, page 403. Rabbi Shlomo Pick (Mail-Jewish 18:77) reports that he personally asked Rav Auerbach, who praised the practice, and Rav Elyashiv, who told him to stay and answer. Rabbi Aryeh Frimer (Mail-Jewish 21:59) quotes his brother Dov as having discussed this with Rav Aharon Lichtenstein who agreed, and stated that such was also his father-in-law’s (Rav Yosef Ber Soloveitchik) opinion. The above all hold that the men should answer with the usual response. Rabbi Dovid Cohen (of Gvul Ya’avetz, Brooklyn) and Rav Dovid Feinstein (MTJ) say that the men should answer as “outsiders” by responding “Baruch u’mevorach Shmo tamid le’olam va’ed.” It thus seems that a great deal of halachic firepower supports the men staying and answering. The idea that men must leave is cited without support in Rav Ellionson’s Ha’Isha V’Hamitzvot.
The proper introduction for the women’s zimun should probably be “Gevirotai  nevarech... Bireshut (imi morati,) gevirotai nevarech.…” Since the men are not part of the zimun, there is no need to get their formal permission.
1. A more complete discussion of this topic can be found in Ari Z. Zivotofsky and Naomi T.S. Zivotofsky, “What’s right with women and zimun,” Judaism, Fall 1993, 42(4)454-464. See also the responsum by Rabbi Yehuda Herzl Henkin in Bnei Banim, Volume 3, number 1 (5758).
2. Some women prefer the more informal “chaverotai” instead of “gevirotai.”
Reprinted from JEWISH ACTION Magazine, Fall 5760/1999 issue