Perhaps one of the most talked about (former) practices of the LDS Church is the practice of plural marriage that existed to varying degrees in the Church from 1831 to about 1904. Plural marriage was officially ended in October 1890 with this declaration from then-President Wilford Woodruff:
Inasmuch as laws have been enacted by Congress forbidding plural marriages, which laws have been pronounced constitutional by the court of last resort, I hereby declare my intention to submit to those laws, and to use my influence with the members of the Church over which I preside to have them do likewise (Official Declaration 1).
President Woodruff's declaration, called the Manifesto, was unanimously accepted by the membership of the Church at that conference. In 1904, finding that some plural marriages had continued to be performed primarily in Mexico and Canada, President Joseph F. Smith called for a prohibition of plural marriage which was also unanimously accepted. Since that time, the Church has not allowed those practicing plural marriage to obtain and/or retain membership.
Paul taught the same doctrine in the ancient church when he taught the Corinthians to, "let every man have his own wife, and every woman have her own husband" (1 Cor. 7:2). The Lord revealed the same law to Joseph Smith in 1831:
Whoso forbiddeth to marry is not ordained of God, for marriage is ordained of God unto man. Wherefore, it is lawful that he should have one wife, and they twain shall be one flesh, and all this that the earth might answer the end of its creation; And that it might be filled with the measure of man... (D&C 49:15-16).
The law of God for man is monogamy. Yet the practice of plural marriage is not without precedent. Abraham, the great patriarch, fathered many nations through the practice of plural marriage (Genesis 16:1-3). Jacob, Abraham's grandson who would later be known as Israel, also practiced plural marriage (Genesis 29:23-30). Moses may have practiced plural marriage (D&C 132:38) and the law of Moses contains provisions for the equal treatment of plural wives (Exodus 21:10), suggesting the practice may have been more widespread (though the practice has always been carefully directed by prophets rather than the general practice of the majority). King David and King Solomon also righteously practiced plural marriage on the whole, despite David's sin with Bathsheba (D&C 132:38-39).
Exceptions to the monogamy rule always have specific purpose. After establishing monogamy as the rule, the Lord taught Jacob, "For if I will, saith the Lord of Hosts, raise up seed unto me, I will command my people; otherwise they shall hearken unto these things [monogamy]" (Jacob 2:30).
So the Lord explained to Joseph Smith:
Abraham was commanded to offer his son Isaac; nevertheless, it was written: Thou shalt not kill. Abraham, however, did not refuse, and it was accounted unto him for righteousness.
Abraham received concubines, and they bore him children; and it was accounted unto him for righteousness, because they were given unto him, and he abode in my law; as Isaac also and Jacob did none other things than that which they were commanded...
David also received many wives and concubines, and also Solomon and Moses my servants, as also many others of my servants, from the beginning of creation until this time; and in nothing did they sin save in those things which they received not of me.
David's wives and concubines were given unto him of me, by the hand of Nathan, my servant, and others of the prophets... and in none of these things did he sin against me save in the case of Uriah and his wife (D&C 132:34-39).
So if the Lord commanded the early members of the LDS Church to practice polygamy to grow the population of the Church, why would he command for polygamy to stop in 1890?
One obvious possibility is because the Church had grown considerably. Though still relatively small, the U.S. Census Bureau estimates church membership had grown to over 188,000 by 1890.
Perhaps another reason can be found in this verse, given long before the practice of plural marriage created persecutions and political problems for the Church. The Lord taught that:
When I give a commandment to any of the sons of men to do a work unto my name, and those sons of men go with all their might and with all they have to perform that work, and cease not their diligence, and their enemies come upon them and hinder them from performing that work, behold, it behooveth me to require that work no more at the hands of those sons of men, but to accept of their offerings (D&C 124:49).
The Church website includes this statement about the end of plural marriage, or polygamy:
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.
Prophets in our day have taught that the family is ordained of God, that marriage is between one man and one woman, and that children are entitled to be reared by a father and mother who honor marital vows with complete fidelity. Throughout history, God has commanded plural marriage as an exception, primarily to allow for rapid population growth. This is done with great care and direction from the Lord himself through the prophets that serve as his mouthpiece. When the goals of plural marriage are accomplished, or when the faithful have done all they can do to be obedient, even if unsuccessfully, plural marriage is again taken from the Church and forbidden by God.
So it is today. The late President Gordon B. Hinckley emphasized 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."
Any groups or individuals who teach or practice plural marriage today are not members of nor affiliated with The Church of Jesus Christ of Latter-day Saints.