Gemara

(Mishnah): Even the poorest Yisrael may not eat until he reclines.

A woman in front of her husband need not recline. If she is esteemed, she must recline.

A son in front of his father must recline.

Question: Must a Talmid in front of his Rebbi recline?

Answer: Abaye taught that in Rabah's house, we would recline on each other's knees. In Rav Yosef's house, he said that we need not recline. The fear of one's Rebbi is like fear of Shamayim.

Question (Beraisa): One reclines in any case, even a Talmid in front of his Rebbi.

Answer: That refers to an apprentice carpenter.

Rishonim

Rambam (Hilchos Chametz 7:7): When one eats on Seder night, he must eat and drink reclining Derech Cherus (like free men).

Hagahos Maimoniyos (2): Avi ha'Ezri says that nowadays we need not recline, for free men do not recline. Just the contrary! Sitting normally is Derech Cherus. However, this is a lone opinion.

Beis Yosef (OC 462 DH v'Chasav): He calls this a lone opinion, for all the Poskim hold that one must always recline, even nowadays.

Rambam (8): A woman need not recline. If she is esteemed, she must recline. A son in front of his father must recline. A Talmid in front of his Rebbi does not recline, unless his Rebbi gave him permission.

Kesef Mishneh: R. Mano'ach says that a distinguished woman is one without a husband, and she is the mistress of the house. Alternatively, she is distinguished through her deeds. She is the daughter of Gedolei ha'Dor, a woman of valor who fears Hash-m. Alternatively, she has slaves, and she need not engage in preparing food or matters of the house.

Rosh (10:20): The Rashbam explains that a woman does not recline due to fear of her husband, to whom she is subservient. If so, a widow or divorcee must recline. The She'altos says that it is not the way of women to recline. This includes even a widow or divorcee. However, it is normal for a distinguished woman to recline. A son in front of his father must recline, even if his father is his Rebbi. Normally, a father teaches his son [and we say that a son in front of his father must recline]. Rav Yosef taught that a Talmid in front of his Rebbi need not recline. This is even if he is not his primary Rebbi, for we needed to establish the Beraisa to discuss an apprentice.

Mordechai (ha'Seder bi'Ktzarah, p.34a column 2 line 6 in standard Gemaros, DH Kasav Ra'avan): Ra'avan says that in their days, they used to sit on beds and recline on the left for pleasure. Therefore, they were obligated to eat reclining. We do not normally do so, so we are Yotzei without reclining. One should not veer right or left.

Bigdei Yesha (33): I would have thought that "Ra'avan" is a textual error, and it should say Avi ha'Ezri (the abbreviations of these names are very similar), but also the Beis Yosef cites this in the name of Ra'avan.

Tosfos (99b DH v'Afilu): One might have thought that an Oni's reclining is not considered reclining, for he has nothing to recline on, and this is not Derech Cherus. The Mishnah teaches that this is not so.

Poskim

Shulchan Aruch (OC 472:2): One should prepare a place to sit so he can recline Derech Cherus.

Mishnah Berurah (7): His head leans left on a bed or bench, and there are pillows under his head by the table.

Kaf ha'Chayim (12): It is a Mitzvah to act with authority on Pesach night. This atones for acting with authority and pride the entire year.

Rema: Even an Oni who has no pillows sits on a bench.

Mishnah Berurah (8): Also if he has no bench and he sits on the ground [like in eastern countries], he must recline on his left.

Shulchan Aruch (4): A woman need not recline, unless she is distinguished.

Gra (DH Ishah): The Rif's text did not say 'in front of her husband'. This shows that all women are exempt, like the She'altos.

Mishnah Berurah (12): A Stam woman never reclines.

Rema: All our women are considered distinguished, but the custom is not to recline, for they rely on Avi ha'Ezri, who says that nowadays one should not recline.

Beis Yosef (DH Ishah): R. Yerucham and the Mordechai bring from Tosfos that all our women are distinguished, and they must recline.

Gra (DH d'Chasav): Nowadays [even] kings do not recline. Women rely also on the She'altos, who says that a woman need not recline.

Kaf ha'Chayim (26): According to R. Mano'ach's reasons, it is hard to understand how the Rema says that all our women are distinguished. The Roke'ach says that it is one whose husband is not particular about her [does not mind if she reclines]. If so, the Rema properly wrote that all our women are distinguished.

Kaf ha'Chayim (28): Keneses ha'Gedolah says that the custom of Sefardi women is to recline. Even in Ashkenazi communities where the custom is not to recline, one who is stringent to recline will be blessed for fulfilling all opinions.

Taz (3) The Bach says that an Avel does not recline, since sitting normally is Derech Cherus. This is the custom.

Magen Avraham (5): An Avel within 12 months [of a parent's death] need not recline, and also an Avel within 30 days after the loss of other relatives, if he did not conduct Shivah before the festival. (If he did, Yom Tov nullifies the law of Sheloshim.)

Mishnah Berurah (13): An Avel within 12 months or Sheloshim must recline, but it is proper not to recline on an honorable bed. Rather, he reclines with a small Shinuy, i.e. on a bed and one pillow, or on another's knees.

Shulchan Aruch (5): A son in front of his father must recline, even if his father is his primary Rebbi.

Gra (DH Afilu): Normally, a father teaches his son Torah. This is why the Torah put fear of a mother before fear of a father (Kidushin 31a).

Magen Avraham (6): Even if the father is his Rebbi, presumably he pardons his honor.

Kaf ha'Chayim (32): Some Acharonim bring the Bach, who says that a son should not recline until he gets explicit permission.

Kaf ha'Chayim (33): If we know that the father does not pardon, Chak Yakov ignores his opinion; the Halachah is based on normal people. Mishbetzos Zahav says that a Safek mid'Rabanan (reclining) does not overrides a Safek mid'Oraisa (Kibud Av v'Em). One should ask permission.

Shulchan Aruch (ibid.): A Talmid in front of his Rebbi does not recline, even if he is not his primary Rebbi, unless his Rebbi gave him permission.

Beis Yosef (DH u'Mah she'Chasav Ela): The Rambam says so (that permission helps). He learns from Rabah, who allowed the Talmidim to recline. We must say that permission helps. Since he saw and was quiet, this is like permission. Rav Yosef said 'you need not do so.' He did not say that it is forbidden!

Taz (4): Why didn't the Gemara answer that the Beraisa obligates a Talmid to recline when the Rebbi gave permission? I answer that the Beraisa connotes that he must recline. A Rebbi's permission does not obligate a Talmid to recline. This shows that a Rebbi need not pardon. If not, we should establish the Beraisa to teach that a Rebbi must give permission!

Note: Perhaps the Taz means that the Beraisa connotes that there is a Chiyuv, either for the Talmid to recline, or for the Rebbi to pardon. Since both are optional, we needed to say that it discusses an apprentice.

Taz (10): Whenever one is exempt from reclining, it is forbidden. This is like we say about Sukah. If one is exempt and fulfills, he is called a Hedyot (commoner). The Maharshal says so.

Magen Avraham (6): The Taz' law is from the Yerushalmi. Be'er Sheva (21) says that one must consider this, for in several cases we are stringent about something we are exempt from.

Mishnah Berurah (15): It says "need not" for parallel structure with the Reisha, but really it is forbidden, for fear of one's Rebbi should be like fear of Hash-m.

Kaf ha'Chayim (34): The Beis Yosef connotes that if the Rebbi sees and is quiet, this is like giving permission. Ma'amar Mordechai says that l'Chatchilah one may not recline without asking permission. B'Di'eved, if he reclined and the Rebbi did not protest, it is as if he gave permission.

Mishnah Berurah (16): If he pardoned, the Talmid must recline.