Polygamy

The Church's website addresses the history and doctrine of polygamy very clearly and openly:

"The family is ordained of God. Marriage between man and woman is essential to His eternal plan. At certain times and for His specific purposes, God, through His prophets, has directed the practice of plural marriage (sometimes called polygamy), which means one man having more than one living wife at the same time. In obedience to direction from God, Latter-day Saints followed this practice for about 50 years during the 1800s but officially ceased the practice of such marriages after the Manifesto was issued by President Woodruff in 1890. Since that time, plural marriage has not been approved by The Church of Jesus Christ of Latter-day Saints and any member adopting this practice is subject to losing his or her membership in the Church.

"The Bible indicates that Abraham, Jacob, and others of the Lord’s servants had multiple wives (see Genesis 16:1–3; 29:23–30; 30:4, 9; Judges 8:30; 1 Samuel 1:1–2). Joseph Smith asked God why He had permitted this practice and was told that God had commanded it for specific purposes. One reason given by the Lord for plural marriage is mentioned in the Book of Mormon: “If I will, saith the Lord of Hosts, raise up seed unto me, I will command my people; otherwise they shall [have only one wife]” (Jacob 2:30; see also v. 27).

"After God revealed the doctrine of plural marriage to Joseph Smith in 1831 and commanded him to live it, the Prophet, over a period of years, cautiously taught the doctrine to some close associates. Eventually, he and a small number of Church leaders entered into plural marriages in the early years of the Church. Those who practiced plural marriage at that time, both male and female, experienced a significant trial of their faith. The practice was so foreign to them that they needed and received personal inspiration from God to help them obey the commandment.
When the Saints moved west under the direction of Brigham Young, more Latter-day Saints entered into plural marriages.

"Influenced by rumors and exaggerated reports, the United States Congress, beginning in 1862, enacted a series of laws against polygamy that became increasingly harsh. By the 1880s many Latter-day Saint men were imprisoned or went into hiding.

"In 1889 in the face of increasing hardships and the threat of government confiscation of Church property, including temples, Wilford Woodruff, President of the Church at the time, prayed for guidance. He was inspired to issue a document that officially ended the sanction of plural marriage by the Church. The document, called the Manifesto, was accepted by Church members in a general conference held in October 1890 and is published in the Doctrine and Covenants as Official Declaration 1 (see also “Excerpts from Three Addresses by President Wilford Woodruff Regarding the Manifesto” following Official Declaration 1).

"Just as the practice of plural marriage among the Latter-day Saints began gradually, the ending of the practice after the Manifesto was also gradual. Some plural marriages were performed after the Manifesto, particularly in Mexico and Canada. In 1904, President Joseph F. Smith called for a vote from the Church membership that all post-Manifesto plural marriages be prohibited worldwide.

"More recently, President Gordon B. Hinckley has reiterated that plural marriage is “against the law of God. Even in countries where civil or religious law allows [the practice of a man having more than one wife], the Church teaches that marriage must be monogamous and does not accept into its membership those practicing plural marriage” (“What Are People Asking about Us?” Ensign, Nov. 1998, 72).

"Groups who teach polygamy today are not part of The Church of Jesus Christ of Latter-day Saints."