The fourth Article of Faith states that members of The Church of Jesus Christ of Latter-day Saints, or Mormons, "believe that the first principles and ordinances of the Gospel are: first, Faith in the Lord Jesus Christ; second, Repentance; third, Baptism by immersion for the remission of sins; fourth, Laying on of hands for the gift of the Holy Ghost."
The Church of Jesus Christ of Latter-day Saints practices baptism by immersion in water. Baptism is typically performed in a special baptismal font and is symbolic of burial and rebirth as a disciple of Jesus Christ. (To reinforce the symbolism of rebirth, baptismal fonts are always below ground level.) Like many Christians, Mormons believe that a person who repents and is baptized has all prior sins remitted.
Baptism is never performed before the eighth birthday. The age of eight was given in latter-day revelation as the age when children become accountable for their sins, meaning that they are able to discern between right and wrong and understand the concept of repentance. If a person is unable to discern between right and wrong (ie. those with severe mental impairment, etc.), they are deemed unaccountable for their sins and do not require baptism, regardless of their age. They are viewed as fully saved through the Atonement of Jesus Christ, as are children who die before the age of accountability. The Book of Mormon and modern revelation specifically forbid the practice of infant baptism. (See Doctrine and Covenants 68:27 and Moroni 8:4-23.)
Baptism is recognized only when performed by someone holding the proper authority, designated to the office of a Priest in the Aaronic Priesthood or a higher office.
Mormons believe that baptism is a necessary prerequisite to entering the kingdom of God in the hereafter, similar to the belief in many Christian sects. This belief presents a problem, however, for the millions of people who have lived and died without the opportunity to even hear of Jesus Christ, much less have the chance to be baptized. For this reason, Mormons believe in the ordinance of Baptism for the Dead. This work is done only in temples, and is performed by someone acting in behalf (proxy) of someone who has died. Mormons believe that such an ordinance as the baptism for the dead, is only of value if the deceased person, who is in spirit, freely chooses to accept the work done on his or her behalf. If the ordinance is accepted by the deceased, he or she will have the opportunity to enter the kingdom of God, the same as if he had the opportunity of being taught and baptized while on earth.