- One should say Al Neharot Bavel before benching after a meal and on days when there’s no tachanun one should say Shir HaMaalot BeShuv Hashem instead. The minhag is to say Shir HaMaalot at Seudot mitzvah as well. 
Obligation of Zimmun
- If three people eat together are obligated to make a Zimmun before benching (making Birkat HaMazon).  Chazal based it on the pasuk “גדלו לה" אתי ונרוממה ה" יחדיו”  and “כי שם ה" אקרא הבו גודל לאלוקונו” .
- Most authorities consider Zimmun to be a rabbinic obligation. 
- Zimmun could be said in any language as the purpose is to introduce the benching orally and join the group together to praise Hashem. 
- Some say that answering Zimmun is considered one of a person’s hundred Brachot every day. 
Who has the obligation?
- It only applies when three or more people eat together. The three conditions to be considered “together” is that those who are eating 1) eat while seated, 2) sit at one table, and 3) eat simultaneously either at the beginning or the end of the meal. 
- If two groups ate in different places in the same house and they could see from one group to another, if they have intent (when they began the meal) to join for Zimmun they may join, however, if if they didn’t have intent, then according to Sephardim they may not join for Zimmun, but according to Ashkenazim it’s a dispute whether they may join for zimmun. 
- If three people aren’t obligated to make Zimmun as they didn’t join their meals, the three can’t do Zimmun. 
- If three ate together and were obligated in Zimmun and one forgot about Zimmun and said Birkat HaMazon then the other two can say zimmun with the third. However, if one of the group answered Zimmun with another group he can’t answer another zimmun of three. 
- If three ate together and one person left he could be called back and Zimmun could be said even if he’s standing by the door next to them, however he should say Birkat HaMazon where he ate. However, if ten people ate together and one left he should be called back and everyone should sit down for Zimmun. 
- If in a school or yeshiva, the students go to lunch at the same time, the group can make Zimmun together even if they sit at separate tables as long as they can see from one table to another. Even if they don’t have enough at each table to make their own Zimmun of ten, they can join together to make a Zimmun of ten. However, it’s preferable that they one time actual say verbally that they intend to eat together. 
A Zimmun of Ten
- If ten people ate bread together, they are supposed to add the word Elokenu in the Zimmun.
- If seven people ate bread and three people ate a kezayit of another food or drank a reviyit of a drink other than water, they can join together for a Zimmun with the insertion of Elokenu. If there are only six people who ate bread they can't make a Zimmun with Elokenu. 
- According to Sephardim, one doesn't have to stand for the word Elokenu in the Zimmun.  Many Ashkenazim have the custom to stand for the word Elokenu in a zimmun of ten, however those who don't stand have what to rely on.
Two who ate together
- Three who ate together must do Zimmun and each one is not allowed to leave the Zimmun. However, if there’s six or more in the Zimmun, the group is allowed to split into two groups of three. If there’s ten then each one isn’t allowed to leave the Zimmun as they are obligated in ZImmun with a mentioning of Hashem’s name. However, if there’s twenty the group may split into two groups of ten. 
- Some say that it’s always preferable to join together in a larger group while others contend that once one is joining in a group of three or ten there’s no obligation to join in a larger group. 
- If three people ate together in the beginning or they finished together (and it’s considered as if they finished together if they still would eat something had if be brought to them) then there’s an obligation of Zimmun. 
- Two who ate together aren't obligated in Zimmun and therefore, they should say Birkat HaMazon to themselves. However, if one of them doesn’t know how to say Birkat HaMazon and the other does, then the one who knows may say it aloud and fulfill the obligation of the one who doesn't know as long as the one saying has intent to fulfill the obligation of the other, and the one listening has intent to fulfill his obligation. 
- According to some it’s crucial that the one who is listening understand the Birkat HaMazon, while others are lenient and say that such is the minhag. 
- If two people ate bread and a third person ate a kezayit of another food, some rishonim hold that they may not join together to make a zimmun, while other rishonim hold that they may join together for a zimmun. Many poskim hold that if the third person doesn't want to eat bread, one may join together for a zimmu 
- If two people eat bread together and a third person ate a kezayit of another food, if one of those who ate bread said Birkat HaMazon without Zimmun, many poskim hold that there is no obligation of Zimmun.
- If two people eat bread together and a third person ate a kezayit of another food, if the one who ate the other food said a Bracha Achrona without Zimmun, there is no obligation of Zimmun.
Who can join a Zimmun
- Women who ate with a group of men who became obligated to make a zimmun are obligated to join in their zimmun. 
- Women who ate together are obligated to make a zimmun and even if their are ten woman they say the zimmun as if they were a group of three. 
- When three women instead of three men say Birkat HaMazon, the word, "Rabotai" is changed to, "Chaverotai".
- The Ashkenazic minhag is not to include children under Bar mitzvah for zimmun, while the Sephardic minhag is to include children of age 6 who know to whom they are saying Birkat HaMazon. Some are Machmir for age 9 in general, or, at least, for zimmun BaShem 
- Those who include Ketanim may do so for both a zimmun of three and a zimmun of ten but not Panim Chadashot or Sheva Berachot.
- The Kattan should have have bread in order to be counted for three.
- Contemporary Poskim agree that this does not extend including one Kattan regardless of the size of zimmun.
- If a Sepharadi, Ashkenazi, and Kattan (Sepharadi) eat bread together, they may make a zimmun if the Sepharadi leads. If they're ten total, consisting of eight Sepharadim, and Ashkenazi, and a Kattan, they Sepharadim may make a zimmun baShem, but the Ashkenazim should answer quietly without Hashem's name in a way that no one will notice the omission.
- Three Ketanim who eat together may not make their own zimmun
- Ashkenazi Ketanim should still answer to a zimmun that they hear according to how much they ate with those bentching.
- Some say that two adult women and a female minor who eat together may make a zimmun.
Zimmun after someone already Benched
- If three people ate bread together, and one forgot to wait for Zimmun, the other two can do Zimmun with the one who already Benched. 
- If three people ate together, two ate bread and one ate a Kezayit of something else or drank a Revi'it of a drink (other than water) are obligated to make Zimmun. 
- If one of three only had a Kezayit of another food or a reviyat of drinks, and one of those who ate bread forgot to wait for Zimmun and Benched, the other one who ate bread can no longer make Zimmun. 
- If one of three only had a Kezayit of another food or a reviyat of drinks, and the one who didn’t eat bread forgot to wait for Zimmun and made Bracha Achrona, the other two who ate bread can no longer make Zimmun. 
- If there’s a doubt whether Zimmun was made or not (or in general a doubt concerning Zimmun) one should be strict to say Zimmun and in a Zimmun of 10 one shouldn’t add Hashem’s name. 
Saying Birkat HaMazon aloud
- The original establishment was that the one doing Zimmun would read the entire Birkat HaMazon out loud. Nowadays, the practice is that everyone say it silently to themselves. 
- According to Ashkenazim it’s preferable to finish the Bracha before the Mezamen (one doing the Zimmun) and then when the Mezamen finishes answer Amen. According to Sephardim there’s no reason to finish before the Mezamen and if one did, nonetheless, one doesn’t answer Amen.  See further on the Birkat HaMazon page.
- If it’s difficult to listen to the entire Birkat HaMazon out loud one should at least listen to the primary part of the Bracha, which according to Sephardim is Birkat Hazimmun (the words “Baruch SheAchalnu…Chayinu”) and according to Ashkenazim is through Birkat HaZan (the first Bracha of Birkat HaMazon). Therefore according to Ashkenazim the Mezamen (even if he is Sephardi) must say the first Bracha out loud and everyone should say it silently along with the Mezamen. 
- According to Ashkenazim, if there’s a large group and those benching will not hear the Mezamen until the end of the first Bracha it’s preferable for the group to separate into groups of three so that it’s possible to hear the Mezamen until the end of the first Bracha. 
- It’s preferable that the Mezamen not use a microphone for Zimmun but rather someone with a loud voice do the Zimmun. 
Procedure and Text of Zimmun
- The Mezamen, who is leading the zimmun, should invite everyone to say Birkat HaMazon. It may be said in any language. If one wants to say this invitation in Hebrew, one should say "Ten Lanu Kos UNivarech" (if one is saying Birkat HaMazon over a cup of wine) or "Bau UNivarech" (if one isn't saying Birkat HaMazon over a cup of wine). If one wants to say this invitation in Aramiac, one should say "Hav Lan UNivarech" or an extended version of this is "Hav Lan VeNivrich LeMalka Iylah Kiddisha", which many Sephardim have the custom of saying. If one wants to say this in Yiddush, the phrase one should say is "Rabbotai Mir Velin Benchin". 
- Those who are participating in the Zimmun should answer to this invitation, according to Ashkenazim, "Yehey Shem Hashem Mivorach MeAtah VeAd Olam", and according to Sephardim, "Shamayim". 
- After the invitation, the mezamen should begin the actual zimmun by saying "Nivarech She'achalnu Meshelo" or with an extended version of "Birshut Malka Iylah Kiddisha UBirshutchem, Nivarach She'achalnu Meshelo", as is the custom of some Sephardim. 
- Those participating in the zimmun should respond "Baruch She'achlnu Meshelo Ubituvo Chayinu." 
- Lastly, the mezamen should conclude "Baruch She'achlnu Meshelo Ubituvo Chayinu."
- If one hears Zimmun but didn’t eat should answer “Baruch UMevurach Shemo Tamid Leolam VaEd” - ברוך ומבורך שמו תמיד לעולם ועד - which has an acronym בושת לו. 
- Kitzur Shulchan Aruch 42:5, Mishna Brurah 1:10,11, Piskei Teshuvot 1:14 in the footnote. See also Rabbi Aryeh Lebowitz on the Ten Minute Halacha.
- S”A 192:1
- Tehilim 34
- Devarim 30. Gemara Brachot 45 quoted by the Mishna Brurah 192:1.
- Pri Megadim (A”A 197:2) writes that most authorities consider zimmun to be of rabbinic obligation. Chaye Adam 48:1 writes that Zimmun is derabbanan and some say it’s Deoritta. Chazon Ish (31:1) argues that Zimmun should be Deoritta.
- Zohar (Balak pg 186b) writes that it’s important to precede benching with “give us a cup to bench” in Hebrew or Aramaic to introduce the benching to bring the kedusha. Mishna Brurah 192:2 quotes this and writes the minhag ashkenaz was to say Zimmun in Yiddish “Rabbotei Mir Velin Benchin”. Kol Bo (Siman 25) emphasizes the group merit of the zimmun.
- Sefer Keysad Mezamnin 1:22
- S”A 193:2 writes that a third person can join two that already started eating if he is “Koveh” (establishes his place) with them. Mishna Brurah 193:21 writes that if one doesn’t eat while sitting and eat at the same table one isn’t considered as being Koveh with the others. Magen Avraham 195:2 and Mishna Brurah 197:3 also include the requirement of sitting at the same table.
- S”A 195:1, Mishna Brurah 195:6
- Rama 193:3 writes that even if three people aren’t obligated in Zimmun it’s preferable that they make Zimmun because of Berov Am Hadrat Melech, that it’s preferable to honor Hashem in multitudes. Mishna Brurah 193:23 writes that the same would apply if there are more than 3 people. However, Magen Avraham in name of many poskim that since one can’t fulfill the Birkat HaMazon for another person one is also not allowed to make a zimmun together. Mishna Brurah 193:24 concludes that the Magen Avraham is more logical.
- S”A 194:1
- Rama 194:1
- S”A 194:2, Mishna Brurah 194:8
- Yalkut Yosef (vol 3 pg 375)
- Shulchan Aruch 192:1
- Shulchan Aruch 197:2
- Halacha Brurah 192:12
- Sh"t Bear Moshe 1:2
- S”A 193:1
- Rama 193:2, Mishna Brurah 193:11
- Mishna Brurah 193:19
- S”A 193:1
- Mishna Brurah 193:5
- Shulchan Aruch 197:3 writes that there are three opinions as to whether two who ate bread may join in a zimmun with a third person who didn't eat bread. The first opinion holds that one may not join together for a three person zimmun unless all three people ate bread. The second opinion holds that they may join together as long as the third person ate mezonot. The last opinion holds that as long as the third person ate anything, they may join together for a zimmun. Shulchan Aruch writes that in order to avoid a dispute one should not allow a third person who doesn't want to eat bread to join with the first two who are eating bread. The Mishna Brurah 197:22, however, writes that the minhag is in accordance with the last opinion allowing a zimmun of three as long as the third person ate something. Halacha Brurah 197:12 also writes that some are lenient. Chacham Ovadia Yosef in Sh"t Yachava Daat 4:13 (in the footnote) quotes the Knesset HaGedola who says that the minhag is to allow a zimmun of three as long as the third person ate something. He explains that the only reason Shulchan Aruch said one should avoid such a zimmun is because in his day people used to listen to the birkat hamazon of the leader of the zimmun, however, nowadays since everyone says the birkat hamazon to themselves such a zimmun is allowed. Mishna Brurah 197:20 notes that the third person must eat at least a kezayit in order to obligate a bracha achrona. Kitzur S"A 45:10, S"A 196:3, and BI"H , Korach, 5 say that ideally the third person joining two others who ate bread for a zimmun should have at least a kazayit of mezonot or wine but it is permissible to join as long as he had a kazayit of any other fruit, vegetable, or drink besides water.
- Beiur Halacha 194:1 s.v. Echad cites the Eliyah Rabba who has a safek about this and concludes that there is no obligation for Zimmin. He quotes the Maamar Mordechai, Birkei Yosef, and Magen Giborim as agreeing. Sefer Keysad Mezamnin (9:22, p. 123) concurs.
- Chaye Adam 48:1 writes that if two people eat bread together and a third person ate a kezayit of another food, if the one who ate the other food said a Bracha Achrona without Zimmun, there is no obligation of Zimmun since the one who ate food other than bread had a non-permanent meal to begin with and has already made a bracha achrona. Sefer Keysad Mezamnin (9:20, p. 122) concurs.
- Kitzur Shulchan Aruch 45:22
- Shulchan Aruch 199:6
- Rama 199:10, Kitzur Shulchan Aruch 45:22
Counting a Kattan in General
The Gemara (Berachot 47b-48a) has a series of Meymrot about being able to make a zimmun with two people and a Sefer Torah, Shabbat, or just by virtue of the fact that they're both Talmidei Chachamim HaMechadedim Zeh et Zeh Bahalacha. Then, the Gemara quotes R' Yochanan that one can be mezamen with a Kattan Poreach, and then it brings a Baraita in support of him. Afterwards, the Gemara says the Halacha does not follow any of the above dinim rather, the Halacha follows Rav Nachman that a Kattan who knows to whom we pray may be counted towards a zimmun. The Gemara continues to bring a story about how Rabbah asked young Abaye and Rava whom we daven to and how they answered correctly.
There are three basic mehalchim in the Rishonim as to how to read the Gemara, resulting in the following Shitot regarding whom we count for a zimmun.
- The Rif (Berachot 35a) quotes Rav Hai Gaon who holds one may count any Kattan who knows whom we daven to, even a nine year old. R' Yonah there also holds this way.
- Rabbeinu Chananel (quoted in the Rif) is of the opinion that a twelve year old, similar to a Mufla Samuch LaIsh, may be counted for a Minyan, if he knows to whom we daven.
- The Rosh (Berachot 7:20) is Machmir for a Yerushalmi that one may never count anyone below the age of thirteen for a Minyan.
The Beit Yosef (199:10) adds that the Hagahot Maimoniot (Berachot 5:6), Samag (Aseh 27), and Maharik (Shoresh 49) also hold like the Rosh, and Rabbeinu Yonah testifies that many of his contemporary Chachamim acted that way. In the end, Maran, in Shulchan Aruch, paskens Kedarko, like the Rif and Rambam against the Rosh, and he explains that it's because zimmun is lesser than a Davar Shebekedushah, so it has room for a kullah. The Darkei Moshe 199:4 says their Minhag is like the Rosh. (See Yabia Omer (4:OC:9:2-3) and 1:OC:42:4 regarding the chiluk between using a Kattan for zimmun and not for Tefillah)
A Lower Age Limit
The Beit Yosef (199:10) discusses further if the Rif has a lower limit for ketanim. One suggestion is that no, whenever he reaches the level of knowing whom we pray to, we count him, while the Rashba (Berachot 48a) and Rivash (Siman 451) both sounds like it's a din in Chinuch. According to the latter, we can only count him from as early as six years old. The assumption is that the Rif's Lashon of age 9-10 was Lav Davka, so he's in agreement with the Rambam who says 7-8. (R' Yonah's Girsa in the Rif was 7-8) LeMaaseh, in Shulchan Aruch, Maran paskens like the Rashba.
The Magen Avraham, as quoted by the Mishnah Berurah (199:24), al atar says from 9-10, like the Lashon of the Rif. The Birkei Yosef (199:4 )says that the Be'er Heitev discusses whether the Magen Avraham meant to disagree with Maran or not, as the Magen Avraham himself writes 6 elsewhere. He says how the Peshat in the Rif is that he's not arguing with the Rambam, but since it's a Safek beDaat HaRif if he mean 9-10 davka, he's Machmir neged Maran. In Shiurei Beracha (199:2) he found the Sefer HaOrah of Rashi that says 9-10 davka beDaat Rav Hai. The Hearot Peat David validates the Chumra but points out that Rashi was just quoting the Rif word for word and makes some question of authorship. See Machatzit HaShekel who's quoted to say similarly.
The Maamar Mordechai (199:4) broadens the discussion about this comment of the Magen Avraham. Every child reaches chinuch at a different age, so the Magen Avraham was just picking one and intended for us to be Somech on what it says in Beit Yosef. He disagrees with the Chidah's reading of the Magen Avraham and thinks that it's Lefaresh and not Lachalok, and he finishes by pointing to 284:4.
The Kaf HaChaim (199:29) and Piskei Teshuvot (199:5) are Machmir for the Chidah.
In Yabia Omer (2:OC:13:11), regarding the how old a child must be for one to answer Amen to his Beracha, Rav Ovadia says that the Chidah strayed from the Kav and there's no need to be Machmir as there's no Beracha Levatala. Therefore, he paskens from six. Elsewhere (8OC 25:8) he adds a Rov that Chareidi kids know whom they're mevarech to and that one can use a Safek Sefeka if he's not sure if the kid is six.
The Ben Ish Chai (Shanah Rishonah Korach 11) says from age nine, but Rav Ovadia (Yabia Omer 9:OC 91:8:3) says Lo Dak (as is Mashma from his Lashon about Maran and the Minhag of Baghdad following Maran), unlike the Kaf HaChaim (199:29) who took it literally. It seems to be Bedaat Maran, so it would depend how you read the Magen Avraham, (like the Chidah or the Maamar Mordechai). Either way, the Ben Ish Chai recommends finding a Gadol if possible.
The Ohr Letzion (2:13:11) distinguishes between a zimmun of three and one of ten. For the former, six years old is sufficient, but one should be machmir for a zimmun bashem for nine years. Rav David Yosef (Halacha Berurah 199:13) disagrees on behalf of his father, though there is no Hasaga in Rav Ovadia's Hearot on the volume (9:108).
Vezot HaBeracha (pg 132) paskens like Chacham Ben Tzion, and Rav Mordechai Eliyahu comments that he disagrees and even allows for zimmun of ten from age six. The latter emphasizes that each Kattan Lifum Chorfeh, everybody reaches that point of understanding at a different age. The fact that Rav Mordechai Eliyahu holds from age six may be a good indication that he read the Ben Ish Chai like Rav Ovadia.
The Birkat Hashem (2:6:25) is also lenient from age six for both 3 and 10, and in footnote 90, he gives three explanations for why we should not follow the Birkei Yosef's Chumra. Firstly, the Chidah might not have meant it LeHoraah, but rather for Yechidim, as he described in Choshen Mishpat 25:6. Next, it's just not Muchrach, and, lastly, had he seen the other Rishonim and understood the Rif, he would have been Chozer Bo.
See further in Yechaveh Daat 4:13 and Yitzchak Yeranen 5:11.
- The Tur (199:10) quotes a dispute between the Rambam (5:7), who says he can be Mitztaref for both a regular zimmun and a zimmun baShem, and R' Peretz, who holds that it's only for a zimmun of ten. The Beit Yosef adds that the latter is also the opinion of Rav Hai Gaon, Tosafot (48a DH veleit), and the Mordechai (Berachot 172) quoting Rabbeinu Tam. He explains that they holds such because we're more strict about zimmun of three than a zimmun of ten, however, the Mordechai records that the Rabbeinu Tam didn't want to rely on his opinion in practice. The Orchot Chaim (39) quotes the Raavad (Temim Deim n. 1) as also holding this way because we go out of our way to enable making a zimmun of ten to praise Hashem with His name but a zimmun of three is insufficient reason to for us to accept the minor. The Shulchan Aruch (199:10) paskens like the Rambam.
- The Kaf HaChaim (199:31) quotes Poskim who say that a Kattan may not, however, count towards a Minyan or Panim Chaddashot for Sheva Berachot. This is also the ruling of Rav Mordechai Eliyahu (in his comments to Vezot HaBeracha pg. 132). See also Yalkut Yosef.
- The Birkat Hashem (vol. 2 ch. 6:25 fn. 90) says that to join a zimmun of three, he has to eat bread or Mezonot, not just a vegetable based on a Safek Sefeka. Although, for ten, even a vegetable is sufficient.
- Rav Yosef Karo (Beit Yosef 199:10) quotes the Kol Bo (Siman 25) that there must always be a Rov Nikar of Gedolim, so a regular zimmun can have a maximum of one Kattan and a zimmun of ten can have up to three.
- The Mishnah Brurah 199:25 quotes the Magen Avraham (199:6) quoting the Shiltei HaGibborim (Berachot 35 1:5) that only one Kattan may be counted. In the Shaar HaTziun (199:14) he says the Magen Avraham and Birkei Yosef both say this bedaat Maran. Upon reading the Birkei Yosef (199:3), it's clear that the Chidah felt Maran actually holds like the Kol Bo, who allows one to use many Ketanim as long as there's a Rov Nikar of Gedolim. Rather, the Birkei Yosef was being Machmir for the Riaz, because many poskim sound that way. This really isn't a Shaylah for Ashkenazim.
- The Kaf HaChaim (199:30), Birkat Hashem (vol. 2 ch. 6:25), Halacha Berurah (199:13), Yalkut Yosef 199:4 (199:6 in Kitzur Shulchan Aruch), and Piskei Teshuvot (199:5) all hold say one may only use one Kattan regardless. The Birkat Hashem quotes many Sepharadi Poskim, such as the Birkei Yosef, Erech HaShulchan (199:2), Kaf HaChaim ibid, Siddur Beit Menuchah, Chessed LeAlaphim, and Yechaved Daat 4:13.
- VeZot HaBeracha (pg. 132) quotes the ruling of R' Chaim Pinchas Sheinberg and Rav Mordechai Eliyahu that if a Sepharadi, Ashkenazi, and Kattan eat together, they may make a zimmun and the Sepharadi should be Mezamen. Moreover, Rav Shlomo Zalman Auerbach holds that if they're eight Sepharadim, an Askenazi, and a Kattan, one of the Sepharadim should make a zimmun BaShem, but the Ashkenazi should answer quietly without the Shem. This is also the ruling of the Piskei Teshuvot (199:5) and it's quoted in Yalkut Yosef (Heb-Eng) there.
- The Perishah had a Girsa in the Tur that ketanim could make their own zimmun, but the Kaf HaChaim (199:18) points out from Maamar Mordechai (199:2) and Yafeh LeLev (199:2) that the Turim printed from the times of Maran and the Bach did not have that Girsa. Neither did the Rambam or Shulchan Aruch themselves. Rav David Yosef (Halacha Berurah 199:14) says that three ketanim who eat together should not make their own zimmun.
- The Piskei Teshuvot (199:5) says that they should answer as appropriate to other people's zimmun based on Chinuch if they ate together with those making a zimmun.
- The Kaf HaChaim (199:21) sounds like they have to be three Gedolot. The Hebrew-English Yalkut Yosef in the footnotes quotes a Maayan Omer (pg 305) that says it's permissible.
- S”A 194:1 writes that if one out of three people in a Zimmun said Birkat HaMazon they can still ma`ke Zimmun to fulfill the obligation of the two and the one who said Birkat HaMazon will not fulfill his obligation because a Zimmun must be said before Birkat HaMazon.
- Mishna Brurah 197:20 writes that if one out of three people ate a Kezayit of a food (other than bread) or drank a reviyat of drinks (other than water), the three people can still make Zimmun.
- Mishna Brurah 197:9
- Mishna Brurah 194 (Beiur Halacha s.v. Echad Mehem) quotes tha Eliya Rabba who is unsure whether the one who ate bread and didn’t make Birkat HaMazon can make Zimmun and concludes that since there’s only one who is obligated (and can fulfill their obligation) they can’t make Zimmun. Such is also the opinion of the Birkei Yosef, Mamer Mordechai, and Magen Giborim.
- Mishna Brurah (Beiur Halacha 197 s.v. Imahem) quotes the Pri Megadim and Chaye Adam who write that if there’s a safek by zimmun one should say it however by the Zimmun of ten people one shouldn’t say it because it includes Hashem’s name.
- Vezot HaBracha (pg 128, chapter 14) quotes that Panim Meirot that the original establishment was that one person say it aloud and everyone listen. However, S”A 183:7 writes that the practice that should be followed nowadays is that one person say it aloud and everyone to follow along Bracha by Bracha.
- S”A and Rama 183:7, Vezot HaBracha (pg 128, chapter 14)
- S”A and Rama 200:1 identify clearly the crucial part of Zimmun, according to S”A it is the Zimmun of Baruch SheAchalnu and according to the Rama it is including the first Bracha. Mishna Brurah 183:28 holds that Ashkenazim should at least say the first Bracha quietly together with the Mezamen and those who have the minhag that everyone just says it to themselves are mistaken. This is also the opinion of Vezot HaBracha (pg 129, chapter 14). Vezot HaBracha (pg 335) quotes Rav Wosner in Kovetz MeBet Levi (Nissan 5758) who defends the minhag slightly. Yalkut Yosef (vol 3 pg 371) says that a Sephardi who is a Mezamen for Ashkenazim should say the first Bracha out loud.
- Mishna Brurah 193:17, Vezot HaBracha (pg 129, chapter 14) also quotes the Chazon Ish who argues but still quotes the Mishna Brurah as the primary opinion.
- Vezot HaBracha (pg 129, chapter 14)
- The Magen Avraham (Intro to 192) quotes the Zohar which says that words of kedusha require preparation and that is the basis for the minhag to invite everyone to say Birkat Hamazon. The Magen Avraham writes that the Ashkenazic minhag was to say it in Yiddish with the words "Rabbotai Mir Velin Benchin". The Mishna Brurah 192:2 adds that it may be said in Hebrew with either the phrase "Ten Lanu Kos UNivarech" (if one is saying Birkat HaMazon over a cup of wine) or "Bau UNivarech" (if one isn't saying Birkat HaMazon over a cup of wine). The Kitzur Shulchan Aruch 45:6 adds that this invitation could be said in Aramiac with the words "Hav Lan UNivarech." Rav Mordechai Eliyahu (comments to Kitzur Shulchan Aruch 45:12) writes that the Sephardic minhag is to say this invitation in Aramiac with the words "Hav Lan VeNivrich LeMalka Iylah Kiddisha."
- The Magen Avraham (Intro to 192), Mishna Brurah 192:2, and Kitzur Shulchan Aruch 45:6 records the Ashkenazic minhag to answer the invitation with the pasuk "Yehey Shem Hashem Mivorach MeAtah VeAd Olam". Rav Mordechai Eliyahu (comments to Kitzur Shulchan Aruch 45:12) writes that the Sephardic minhag is that those participating in the Birkat HaMazon answer "Shamayim," meaning, that this should be done with the permission of heaven.
- Shulchan Aruch 192:1 writes that the mezamen should begin the zimmun by saying "Nivarech She'achalnu Meshelo". Rav Mordechai Eliyahu (comments to Kitzur Shulchan Aruch 45:12) writes that the Sephardic minhag is the mezamen starts the zimmun with the words "Birshut Malka Iylah Kiddisha UBirshutchem, Nivarach She'achalnu Meshelo."
- Shulchan Aruch 192:1 writes that those participating in the zimmun should respond "Baruch She'achlnu Meshelo Ubituvo Chayinu."
- Shulchan Aruch 192:1 writes that the mezamen should conclude "Baruch She'achlnu Meshelo Ubituvo Chayinu."
- S”A 198:1, Kitzur Shulchan Aruch 45:20, Vezot HaBracha (pg 129, chapter 14)