Note: This is a good overview of the Hilchos Melech HaMashiach (i.e. the laws governing King Messiah). As in most areas, Jews do not always agree on this topic. This piece is a balanced presentation that I believe is worthy of serious study. Enjoy.
1. In future time, the King Mashiach  will arise and renew the Davidic dynasty, restoring it to its initial sovereignty. He will rebuild the [Beis Ha]Mikdash and gather in the dispersed remnant of Israel. Then, in his days, all the statutes will be reinstituted as in former times. We will offer sacrifices and observe the Sabbatical and Jubilee years according to all their particulars set forth in the Torah.
Whoever does not believe in him, or does not await his coming, denies not only [the statements of] the other prophets, but also [those of] the Torah and of Moshe, our teacher, for the Torah attests to his coming, stating: [Devarim 30:3-5]
And the Lord your G-d will bring back your captivity and have compassion upon you. He will return and gather you [from among all the nations].... Even if your dispersed ones are in the furthest reaches of the heavens, [from there will G-d gather you in].... G-d will bring you [to the land]....
These explicit words of the Torah include all that was said [on the subject] by all the prophets.
There is also a reference [to Mashiach] in the passage concerning Bilaam, who prophesies about the two anointed [kings]: the first anointed [king] , David, who saved Israel from her oppressors, and the final anointed [king] who will arise from among his descendants and save Israel [at the End of Days] . The following [quoted] phrases are from that passage: [Bamidbar 24:17-18]
"I see it, but not now" - This refers to David; "I perceive it, but not in the near future" - This refers to King Mashiach.
"A star shall go forth from Yaakov" - This refers to David; "and a staff shall arise in Israel" - This refers to King Mashiach.
"He shall crush all of Moab's princes" - This refers to David, (as it is written [II Shmuel 8:2], "He smote Moab and measured them with a line"); "he shall break down all of Seth's descendants" - This refers to King Mashiach, (about whom it is written [Zechariah 9:10], "He will rule from sea to sea").
"Edom will be demolished" - This refers to David, (as it is written [Cf. II Shmuel 8:6 and 8:14], "Edom became the servants of David"); "his enemy, Seir, will be destroyed" - This refers to Mashiach, (as it is written [Ovadiah 1:21], "Saviors will ascend Mount Zion [to judge the mountain of Esau....]").
2. Similarly, in regard to the cities of refuge, it is stated [Devarim 19:8-9], "When G-d will expand your borders... you shall add three more cities." This command has never been fulfilled. [Surely,] G-d did not give this command in vain, [and thus the intent was that it be fulfilled after the coming of Mashiach]. There is no need to cite prooftexts on the concept [of the Mashiach] from the words of the prophets, for all [their] books are filled with it.
3. One should not entertain the notion that the King Mashiach must work miracles and wonders, bring about new phenomena within the world, resurrect the dead, or perform other similar deeds. This is [definitely] not true.
[A proof can be brought from the fact that] that Rabbi Akiva, one of the greatest Sages of the Mishnah, was one of the supporters of King Ben Koziva, and would describe him as the King Mashiach. He and all the Sages of his generation considered him to be the King Mashiach until he was killed because of [his] sins. Once he was killed, they realized that he was not [the Mashiach]. The Sages did not ask him for any signs or wonders.
[Rather,] this is the main thrust of the matter: This Torah, with its statutes and laws, is everlasting. We may neither add to them nor detract from them. 
4. If a king will arise from the House of David who delves deeply into the study of the Torah and, like David his ancestor, observes its mitzvos as prescribed by the Written Law and the Oral Law; if he will compel all of Israel to walk in [the way of the Torah] and repair the breaches [in its observance]; and if he will fight the wars of G-d; - we may, with assurance, consider him Mashiach.
If he succeeds in the above, builds the [Beis Ha]Mikdash on its site, and gathers in the dispersed remnant of Israel, he is definitely the Mashiach. 
He will then perfect the entire world, [motivating all the nations] to serve G-d together, as it is written [Zephaniah, 3:9], "I will make the peoples pure of speech so that they will all call upon the Name of G-d and serve Him with one purpose."
1. One should not entertain the notion that in the Era of Mashiach any element of the natural order will be nullified, or that there will be any innovation in the work of creation. Rather, the world will continue according to its pattern.
Although Yeshayahu [Yeshayahu 11:6] states, "The wolf will dwell with the lamb, and the leopard will lie down with the young goat," these [words] are an allegory and a riddle. They mean that Israel will dwell securely together with the wicked gentiles who are likened to wolves and leopards, as in the verse [Yirmeyahu 5:6], "A wolf of the deserts despoils them, a leopard watches over their cities." [In this era, all nations] will return to the true faith and no longer plunder or destroy. Instead, at peace with Israel, they will eat that which is permitted, as it is written [Yeshayahu 11:7], "The lion shall eat straw like the ox."
Similarly, other prophecies of this nature concerning Mashiach are analogies. In the Era of the King Mashiach, everyone will realize what was implied by these metaphors and allusions.
2. Our Sages taught: [Berachos 34b] "There will be no difference between the current age and the Era of Mashiach except [our emancipation from] subjugation to the [gentile] kingdoms."
The simple meaning of the words of the prophets appears to imply that the war of Gog and Magog [Yechezkal ch. 38] will take place at the beginning of the Messianic age. Before the war of Gog and Magog, a prophet will arise to rectify Israel's conduct and prepare their hearts [for the Redemption], as it is written: [Malachi 3:23] "Behold, I am sending you Eliyah(u)  [before the advent of the great and awesome Day of G-d]."
He will not come [in order] to declare the pure, impure, nor to declare the impure, pure; nor [will he come in order] to disqualify the lineage of those presumed to be of flawless descent, nor to validate lineage which is presumed to be blemished. Rather, [he will come in order] to establish peace in the world; as [the above prophecy] continues [Malachi 3:24], "He will bring back the hearts of the fathers to the children."
Some of the Sages say that Eliyahu will appear [immediately] before the coming of Mashiach.
All these and similar matters cannot be [clearly] known by man until they occur, for they are undefined in the words of the prophets. Even the Sages have no established tradition regarding these matters, beyond what is implied by the verses; hence there is a divergence of opinion among them.
In any case, neither the sequence of these events nor their precise details are among the fundamental principles of the faith. One should not occupy himself at length with the aggadot and midrashim that deal with these and similar matters, nor should he deem them of prime importance, for they bring one to neither the awe nor the love [of G-d].
Similarly, one should not try to calculate the appointed time [for the coming of Mashiach]. Our Sages declared: [Sanhedrin 97b] "May the spirits of those who attempt to calculate the final time [of Mashiach's coming] expire!" Rather, one should await [his coming] and believe in the general conception of the matter, as we have explained.
3. During the Era of the King Mashiach, once his kingdom has been established and all of Israel has gathered around him, the entire [nation's] line of descent will be established on the basis of his words, through the prophetic spirit which will rest upon him. As it is written [Loc. cit., v. 3], "He shall sit as a refiner and purifier."
He will purify the lineage of the Levites first, stating that "This one is a priest of defined lineage" and "This one is a Levite of defined lineage." Those whose lineage he does not recognize will be relegated to the status of Israelites. This is implied by the following verse: [Ezra 2:63] "The governor said to them, '[They shall not eat of the most holy things] until a priest arises [who will wear] the Urim and Tumim.'" From this verse one can infer that the genealogy of those presumed to be of unquestioned [priestly and levitical] lineage will be traced by means of the prophetic spirit, and those found to be of such lineage will be made known.
He will define the lineage of the Israelites according to their tribe alone; i.e., he will make known each person's tribal origin, stating that "This one is from this tribe" and "This one is from another tribe." However, concerning a person who is presumed to be of unblemished lineage, he will not state that "He is illegitimate," or "He is of slave lineage," for the law rules that once a family has become intermingled [within the entire Jewish people], they may remain intermingled.
4. The Sages and prophets did not yearn for the Messianic Era in order that [the Jewish people] rule over the entire world, nor in order that they have dominion over the gentiles, nor that they be exalted by them, nor in order that they eat, drink and celebrate. Rather, their aspiration was that [the Jewish people] be free Ito involve themselves] in Torah and its wisdom, without anyone to oppress or disturb them, and thus be found worthy of life in the World to Come, as we explained in Hilchos Teshuvah.
5. In that Era there will be neither famine nor war, neither envy nor competition, for good things will flow in abundance and all the delights will be as freely available as dust. The occupation of the entire world will be solely to know G-d. The Jews will therefore be great sages and know the hidden matters, and will attain an understanding of their Creator to the [full] extent of human potential; as it is written [Yeshayahu 11:9], "For the world will be filled with the knowledge of G-d as the waters cover the ocean bed."
- In the original Hebrew, HaMelech HaMashiach (lit., "the anointed king"); i.e., the Messianic King.]
- In the original Hebrew, the word here translated "anointed [king]" is simply HaMashiach (lit. "the anointed one"); i.e., the Messiah. It is used interchangeably with the earlier phrase.]
- At this point, before being censored by medieval Christian authorities, the Rambam's original text continued: "...and save Israel from the hand's of Esav's descendants. This and two other such deletions have been copied verbatim in these footnotes from the celebrated Yemenite manuscript in the hands of Chacham Yosef Kapach of Jerusalem. (See footnotes 4 and 5, below.)]
- At this point, the uncensored original text continued as follows: "Whoever adds to [the mitzvoth] or detracts from them, or misinterprets the the Torah, implying that the mitzvos are not intended to be understood literally, is surely a wicked imposter and a heretic."
- The whole of the following passage was deleted from most of the editions published since the Venice edition of 1574.
"If he did not succeed to this degree or he was killed, he surely is not [the redeemer] promised by the Torah. [Rather,] he should be considered as all the other proper and legitimate kings of the Davidic dynasty who died. G-d only caused him to arise in order to test the multitude. As it is written [Daniel 11:35], "Some of the wise men will stumble, to purge, to refine, and to clarify, until the appointed time, for it is yet to come."
"Jesus of Nazareth who aspired to be the Mashiach and was executed by the court was also spoken of in Daniel's prophecies [Daniel 11:14], "The renegades among your people shall exalt themselves in an attempt to fulfill the vision, but they shall stumble."
"Can there be a greater stumbling block than [Christianity]? All the prophets spoke of Mashiach as the redeemer of Israel and their savior, who would gather their dispersed ones and strengthen their [observance of] the mitzvos. In contrast [the founder of Christianity] caused the Jews to be slain by the sword, their remnants to be scattered and humiliated, the Torah to be altered, and the majority of the world to err and serve a god other than the L-rd."
"Nevertheless, the intent of the Creator of the world is not within the power of man to comprehend, for [to paraphrase Yeshayahu 55:8] His ways are not our ways, nor are His thoughts our thoughts. [Ultimately,] all the deeds of Jesus of Nazareth and that Ishmaelite [i.e. Mohammed] who arose after him will only serve to pave the way for the coming of Mashiach and for the improvement of the entire world, [motivating the nations] to serve G-d together, as it is written [Zephaniah 3:9], "I will make the peoples pure of speech so that they will all call upon the Name of G-d and serve Him with one purpose."
"How will this come about? The entire world has already become filled with talk of [the supposed] Messiah, as well as of the Torah and the mitzvos. These matters have been spread among many spiritually insensitive nations, who discuss these matters as well as the mitzvos of the Torah. Some of them [i.e. the Christians] say: "These commandments were true, but are not in force in the present age; they are not applicable for all time." Others [i.e. the Moslems] say: "Implied in the commandments are hidden concepts that cannot be understood simply; the Messiah has already come and revealed them."
"When the true Messiah king will arise and prove successful, his [position becoming] exalted and uplifted, they will all return and realize that their ancestors endowed them with a false heritage; their prophets and ancestors cause them to err."
- The name of the prophet is occasionally spelled, as in this verse, without the final letter vav.
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