Aleinu

Is it an obligation to bow during aleinu?

Shalom!

Thank you for your question.

According Halacha, one is to bow when reciting Aleinu. This is so important that there are even those who say that one who forgot to bow must recite Aleinu over again, although this is not Le'halacha.

There are differing customs on how the bowing is performed, which is to be done when reaching the words “ va’anachnu kor’im ” (“and we kneel”):

Some just bow their head slightly. as brought in the Ben Ish Chai Parshat Ki Siso (ot 18) and the shut Torah Lishmoh siman 48.

However, Lehalcah the optimal way is first bend their knees and then bow from the waist, since this is brought by the Magen Avraham siman 132 seif katan 3, and the Be'er Heitev seif Katan 4 in the name of the Arizal and it is also brought in the siddur Ya'vets at the end of the morning prayer. Therefore, Harav fried Shelita writes that Le'halcha one should optimally bow like by the Bracha of Modim.

That being said, there have been sages in the past who did not bow during Aleinu at all although common custom is not like this view. However, even those who do not bow during Aleinu agree that one is required to bow when reciting Aleinu in a place where everyone bows as one is not permitted to deviate from the congregational custom. One with no custom should definitely bow during Aleinu

Allow me to add a few interesting points on the Aleinu prayer. There is an ancient tradition that Joshua composed the Aleinu prayer after the conquest of Jericho. Others suggest that it was likely composed, or at least completed in its current form by the Talmudic sage Rav in the third century Babylon. There is even a theory that it is from the second Temple era. It is interesting to note that Aleinu was originally intended to be recited as part of the Mussaf prayer of Rosh Hashana. It was later adopted for daily use.

Rema, OC 132:2; Mishnah Berura 132:9; Shulchan Aruch Harav, OC 109:2; Kolbo 16; Machzor Vitri