Are polygamists Mormon?
The Mormon church does not consider members of the Fundamentalist Church of Jesus Christ of Latter-day Saints (FLDS) — the most widely-known modern group that continues to practice plural marriage — or any other polygamist sect to be Mormons, and practicing polygamy is grounds for excommunication. Nearly all of the polygamist groups in the intermountain west are technically schismatic Mormon groups. They accept the Book of Mormon as scripture and embrace LDS doctrines, mainly differing from the church headquartered in Salt Lake City over the issue of whether the manifesto that proscribed plural marriage was a revelation and over who ought to be presiding over the church.
