In the Mormon religion, also known as The Church of Jesus Christ of Latter-day Saints, the Aaronic Priesthood is the lesser priesthood referred to in the Bible in Hebrews 7:11-12, “If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?” This priesthood is also called the Levitical Priesthood, because under the Law of Moses one of the tribes of Isreal known as the Levites were the priests in this priesthood. Another name for this priesthood is the Preparatory Priesthood, because it prepares men to receive the greater priesthood, and sacred ordinances.

After the death of Christ and his Apostles, the world lost the priesthood. This is known as the Great Apostasy. This period lasted for hundreds of years. Then on May 15, 1829 the Aaronic Priesthood was restored again to the earth. John the Baptist appeared to Joseph Smith and Oliver Cowdery as a heavenly messenger and conferred the Aaronic Priesthood on them. It is known that John the Baptist held the Aaronic Priesthood during his life because he had the authority to baptize.

There are four offices in the Aaronic Priesthood; Deacon, Teacher, Priest and Bishop. Today young men do not have to be of a certain tribe to minister in this priesthood. It is given to every worthy male. Young men usually are ordained as deacons at twelve years old, as teachers at fourteen years old, and as priests at sixteen years old. A young man must be at least twelve to receive the priesthood, but there is no maximum age for when a man can receive the priesthood, but it is always received in order; Deacon, Teacher, then Priest.

The Aaronic Priesthood duties are related to temporal or outward ordinances of Christ’s gospel. Each office within the Aaronic Priesthood has specific duties. Deacons are to assist the other offices in any way necessary, pass the sacrament, gather fast offerings, teach and invite all to come unto Christ. Teachers are to watch over the members of the Church and to strengthen and help the members. Priests are to teach, baptize and bless the sacrament. Deacons cannot perform the duties of Priests such as baptizing or blessing the sacrament because they hold a lesser office, but Priests can perform the duties of a Deacon or Teacher. The Bishop holds a special role in the Aaronic Priesthood. There is only one bishop in each ward, or congregation. A Bishop is the leader of the Aaronic Priesthood of that ward. He is responsible for the welfare of the people of the congregation and is to organize the other Aaronic Priesthood holders so that the needs of the people are met.

Other Links:
Restoration of the Aaronic Priesthood Site
Aaronic Priesthood Restoration Site
Aaronic Priesthood
Organization and Government: Priesthood: LDSFAQ