It is considered a great mitzva to prepare and partake of a special meal following the conclusion of Shabbat. This meal is referred to as the "melave malka" meal which means "escorting the queen". It is also frequently referred to as "the fourth meal", linking it to the three meals which one is required to eat over the course of Shabbat. The purpose of this meal is to accord honor to the departing Shabbat similar to the feast one would hold in honor of a departing dignitary.
The melave malka meal should preferably be held within fours hours following the conclusion of Shabbat though it may be held any time until midnight. Under extenuating circumstances one can still fulfill the mitzva of eating the melave malka meal until dawn Sunday morning. Although one may not have an appetite to eat yet another meal following the conclusion of a gastronomically filled Shabbat one should nevertheless make every effort to do so. So too, one should make the effort to eat melave malka even if one is ill.
One should endeavor to recite the hamotzi blessing over two whole loaves at the melave malka meal just as is done on Shabbat. If one is too full to eat bread, one can eat cake or even fruit in honor of the melave malka. It is also recommended that one eat meat or fish at this meal as well as garlic and onions along with a hot drink. Ultimately however, partaking of the melave malka meal is essentially optional and not an outright obligation. Some authorities say that if need be one can discharge the melave malka '"meal"' with merely a hot drink.
The melave malka meal is also referred to as "the meal of King David". This is because God had revealed to David that he would die on a Shabbat. As such, David would hold a celebratory meal each week at the conclusion of Shabbat in order to thank God that he was alive and for being given the opportunity to live at least another week. One should eat the melave malka while still wearing one's Shabbat clothes. Some authorities allow one to eat meat for the melave malka even during the "nine days" when eating meat is ordinarily forbidden.
We are taught that the additional soul one receives each Shabbat remains until one has eaten the melave malka meal. Incidentally, it is also taught that after every Shabbat one's additional soul is summoned before God and is asked which foods it enjoyed eating over the course of Shabbat. The melave malka meal serves as the intermediary to ensure that all meals one eats during the coming week will be imbued with holiness. There is an opinion that one can discharge one's melave malka meal by extending one's seudat shlishit into the night if one is sure to eat some bread after dark. Other authorities, however, argue that the melave malka meal may only take place after havdalla has been recited.
There is a bone in our bodies known as the "luz" bone which is located at the base of our skull at the place where the tefillin knot lies. It is believed that this is the primordial and indestructible bone from where man was created and the point from where one's resurrection will take place at the coming of the Mashiach. The luz bone merited this unique status from the fact that it was the only part of the body which did not derive any benefit from the Tree of Knowledge. It is taught that this bone derives its nourishment exclusively from the melave malka meal. Even in the event that a body had been cremated or undergone other severe trauma the luz bone can never be fully destroyed.
It is customary to set one's table in a lavish manner complete with candles as if the melave malka was actually a Shabbat meal. It is considered praiseworthy to reserve a costly delicacy especially for this meal or to at least dine on foods which were prepared specifically for the melave malka meal. It is also advised to eat one's favorite foods at this meal. One who completely dismisses the melave malka meal and never partakes of it is considered as "one who was never created". Women should also be sure eat the melave malka meal.
It is taught that the well of Miriam, which accompanied the Jewish people throughout their wandering in the desert and supplied them with water, flows into our water supply each Motzai Shabbat. As such, it is believed that drinking water Motzai Shabbat has beneficial healing properties. Eating the melave malka meal is also said to be a segula for women to experience an easy delivery in childbirth. It is customary to tell stories of the Baal Shem Tov, as well as other tzadikkim, on Motzai Shabbat. It is also fitting to bless one's children as well as to seek the blessings of great rabbis on Motzai Shabbat.One should also be sure to bathe or shower in hot water every motzai shabbat. Some authorities recommend not writing tefillin or Torah scrolls on Motzai Shabbat, though this is not halachically required.
 Shabbat 119b, Rambam Shabbat 30:5, O.C. 300:1
 Aruch Hashulchan O.C. 300:2
 Pitchei Olam U'metamei Hashulchan 300:1, Kaf Hachaim (Rav Palagi) 31:59
 Ben Ish Chai;Vayeitzei
 Orchot Chaim of the Rosh 69
 Ma'aseh Rav 39
 Pitchei Olam U'metamei Hashulchan 300:1. The Chazon Ish has been quoted as saying that those who don't eat bread for melave malka will "regret it" in the Next World.
 Shaarei Teshuva 300:1
 Magen Avraham O.C. 300
 Aruch Hashulchan 300:3
 Teshuvot V'hanhagot 2:166
 Aruch Hashulchan 300:4
 Shulchan Aruch Harav 300:1, Mishna Berura 300:2
 Piskei Teshuvot 300:1
 Shabbat 30a
 Taamei Haminhagim 425
 Kaf Hachaim 300:14
 Teshuvot V'hanhagot 2:166
 Shaarei Teshuva 300:1, Machzik Beracha 300:2
 Zohar;Parshat Emor
 Kaf Hachaim 300:2
 Be'er Heitev 300:1, Aruch Hashulchan 300:3
 Kaf Hachaim 300:11, Rivevot Ephraim 6:170
 Beit Yosef 300, Kaf Hachaim 300:1
 Kaf Hachaim (Rav Palagi) 31:62
 Aruch Hashulchan O.C. 300:2
 Elya Rabba 300:1
 Kaf Hachaim (Rav Palagi) 31:60
 Shabbat 119b, Ta'amei Haminhagim 425
 Be'er Heitev 300:1
 Kaf Hachaim (Rav Palagi) 31:61
 Yesodei Yeshurun 5 p.344, Rivevot Ephraim 1:275
 Kaf Hachaim 300:4
 Kaf Hachaim (Rav Palagi) 31:63
 Shabbat 119a;Rashi
 Piskei Teshuvot 300:2