Celestial marriage (also called the New and Everlasting Covenant and Eternal Marriage) is a doctrine unique to Mormonism, particularly The Church of Jesus Christ of Latter-day Saints (LDS Church) and branches of Mormon fundamentalism. It exists also in the Orthodox Catholic Church, in which it serves to unite a woman and a man in eternal union before God. It refers to the first centuries of the church, where spiritual union of spouses in the first sacramental marriage was eternal. In spite of the fact that in Roman Catholic Church marriage is only lifelong, "till death take us part", Pope John Paul II in his book Man and Woman He Created Them: A Theology of the Body (Pauline Books & Media, 2006) tells that there won't be marriage in its procreative bond but there will exist eternal and full spiritual union between spouses in Kingdom of God. What's more he bases on Matthew 22:30.

Celestian Marriage is an ordinance associated with a covenant that always takes place inside temples by those authorized to hold the sealing power. As such, the only people allowed to enter the temple are those who hold an official temple recommend. In the marriage ceremony a man and a woman make covenants to God and to each other and are said to be sealed as husband and wife for time and all eternity. The Latter-Day Saint distinguishes itself on this point from many other religions. The belief is that the marriage relationships and covenants made in this life will continue to be valid in the next life.

In the 19th century the term celestial marriage often referred specifically to the practice of plural marriage, a practice which the LDS Church abandoned in 1890. Plural marriage is still continued by Mormon fundamentalists not affiliated with the LDS Church, and is referred to as celestial marriage.

In the current LDS Church, both men and women may enter a celestial marriage with only one partner at a time. A man may be sealed to more than one woman; if his wife dies, however, he may enter another celestial marriage, and be sealed to both his living wife and deceased wife or wives. Many Mormons believe that all these marriages will be valid in the eternities and the husband will live together in the afterlife as a family with all to whom he was sealed. On page 72 of the 1998 edition of the Church Handbook of Instructions, the LDS Church clarified that a woman may also be sealed to more than one man. A woman, however, may not be sealed to more than one man while she is alive. She may only be sealed to subsequent partners after she has died. Church leaders have not clarified if women in such circumstances will live in a polyandrous relationship in the afterlife. However, proxy sealings, like proxy baptisms, are merely offered to the person in the afterlife, indicating that the purpose is to allow the woman to choose the right man to be sealed to, as LDS doctrine forbids polyandry. According to LDS belief, the celestial marriage covenant, as with other covenants, requires the continued righteousness of the couple to remain in effect after this life. If only one remains righteous that person is promised a righteous eternal companion in eternity.