In Christian theology, pre-existence is the belief that each individual human soul existed before conception, and at conception (or later, depending on when it is believed that the soul enters the body) God places one of these pre-existent souls in the body. Pre-existence is in contrast to traducianism and the more widely accepted version of creationism which both hold that the individual human soul does not come into existence until conception or later.
See also: Accounts of pre-mortal existence
The concept of pre-existence is an early and fundamental doctrine of Mormonism. In 1833, early in the Latter Day Saint movement, its founder Joseph Smith, Jr. taught that just as Jesus Christ was coeternal with God the Father, "Man was also in the beginning with God. Intelligence, or the light of truth, was not created or made, neither indeed can be." (LDS D&C 93:21-23.)
In 1844, Smith taught:
After Smith's death, the doctrine of pre-existence was elaborated by some other Latter Day Saint leaders, primarily within the Church of Jesus Christ of Latter-day Saints and its breakoffs. Although the "mind" and "intelligence" of humanity were still considered to be co-eternal with God, and not created, Brigham Young introduced the idea that the "spirit", which he distinguished from the "mind" or "intelligence", was indeed created and not co-eternal with God. Young postulated that we each had a pre-spirit "intelligence" that later became part of a spirit "body", which then eventually entered a physical body and was born on earth. In 1857, Young stated that every person was "a son or a daughter of [the Father]. In the spirit world their spirits were first begotten and brought forth, and they lived there with their parents for ages before they came here." 4 J.D. 218.
Among Latter-day Saints (Utah Mormons), the idea of "spirit birth" was described in its modern doctrinal form in 1909, when the First Presidency of the Church of Jesus Christ of Latter-day Saints issued the following statent:
This description is widely-accepted by modern Latter-day Saints (Utah Mormons). However, among other Latter Day Saint denominations, there are differences of opinion as to the nature of the pre-existence.