Mormons believe their church is the one and only true church established by Jesus Christ in New Testament times.
That church, however, was hopelessly corrupted soon after Jesus ascended into heaven, which led to what Mormons call the Great Apostasy that resulted in the misinterpretation and misteaching of many scriptures.
Mormons believe that the true church had to be restored, through the priesthood, a term which refers to male believers who have the authority to act in the name of God.
Here's a short, admittedly incomplete, history of the Mormon movement:
In 1823, 17-year-old Joseph Smith Jr., a young man who practiced so-called "black magic" to find buried treasures in his hometown of Palmyra, N.Y., was visited by the angel Moroni, who told him of a sacred text written on solid-gold plates buried on a nearby hill.
Eventually, Joseph was able to uncover and transcribe these plates, which became the Book of Mormon, the history of how an ancient Hebrew tribe left Jerusalem 600 years before the birth of Christ and traveled to North America.
This tribe eventually split into two rival groups, the Nephites, the fair-skinned good guys, and the Lamanites, who were not favored by God.
According to the Book of Mormon, Jesus, after his resurrection, visited North America to share his gospel with the two clans, who then quit fighting for a while, but eventually started up again.
The dark-skinned Lamanites eventually slaughtered all the Nephites, and became the ancestors of modern American Indians.
Mormon was a wise leader of the doomed Nephites, and his son was Moroni, who would eventually return as an angel to reveal to Joseph Smith that the church he would found would lead to the salvation of mankind.
But the greatest promise of the Mormon religion was that each follower would have an extraordinarily intimate relationship with God. Divine revelation, starting with Joseph Smith, was a bedrock of the new religion he founded in 1830.
Mormons believe God has not always been the supreme being of the universe, but attained that status through righteous living and persistent effort. They believe God the Father has a "body of flesh and bones as tangible as man's."
Mormon leaders also have taught that Jesus' incarnation was the result of a physical relationship between God the Father and Mary. They believe Jesus is a God, but that any human can also become a god.
While there are far too many differences with Christianity to list here, for most Christians, Mormonism is seen as a false religion. Mormons, in turn, believe present-day Christians follow hopelessly corrupted doctrines and teachings and that as Latter-Day Saints, they are the true sons and daughters of Israel.
Another sacred text for Mormons is the revelation to Smith known as the Doctrine and Covenants. Section 132 of this text has become the rallying cry for polygamous fundamentalists. In it, the prophet described plural marriage as part of "the most holy and important doctrine ever revealed to man on earth."
After being arrested, Joseph Smith was murdered in Illinois in 1844 by a mob.
Brigham Young, who also had multiple wives, later became leader of Smith's church, and led the Saints to the Great Basin of Utah.
The issue of polygamy became a national scandal, pitting the federal government against the LDS church, and kept Utah from gaining statehood.
In 1890, LDS leaders gave up polygamy.
The church, cleaned up of this nefarious practice, moved from being considered a wild-eyed sect of crackpots into its present standing as a pro-family, conservative, entirely sensible American faith.
The church today excommunicates any member either practicing or openly advocating the practice of polygamy and believes that it is improper to call any of these splinter polygamous groups "Mormon."
But after the LDS church forsook polygamy, various splinter groups left to continue the practice, which persists today in Utah and neighboring states. Polygamist churches of Mormon origin are called Mormon fundamentalist.
Mormon fundamentalists believe the church sold them out to gain acceptance. Modern-day polygamists believe that the LDS church, in forsaking Section 132, has lost its way.
Fundamentalists also cite another part of the Doctrine and Covenants, Section 85, in which it was revealed to Joseph Smith that "one mighty and strong" will be sent to Earth to restore the Mormon church to its rightful place, which they say would include Joseph Smith's "most holy and important doctrine" of polygamy.
Both FLDS and mainstream Mormons believe that Smith was a prophet on the order of Moses, and believe in the same "scriptures" that Smith said were revealed to him.
There are between 30,000 and 40,000 FLDS polygamists living in the American West, Canada and Mexico — less than 1 percent of the LDS worldwide church.