Same Sex Marriage
It should be noted that The Church of Jesus Christ of Latter-day Saints has always been in favor of gay rights but against changing the definition of marriage. The Church championed "civil unions" with all rights but met with resistance both from gay activists and far right conservatives. By championing gay rights in Utah, along with protecting religious rights, the state has become an example of tolerance for the rest of America. Salt Lake City is considered one of the most gay-friendly cities in the U.S.
Principles and Doctrine
Teachings in the restored gospel of Jesus Christ declare that "God has commanded that the sacred powers of procreation are to be employed only between man and woman, lawfully wedded as husband and wife" and further that "Children are entitled to birth within the bonds of matrimony, and to be reared by a father and a mother." 
President Russell M. Nelson stated the Church's position supporting a constitutional amendment in the following statement on June 5, 2006, in Washington, D.C.:
The Church of Jesus Christ of Latter-day Saints is pleased to be represented in this significant cause. While those of us here today represent a broad spectrum of religious diversity, we are firmly united in our declaration that marriage of a man and a woman is ordained of God. The sanctity of marriage and family constitutes the spiritual undergirding of lasting and successful societies.
Together we share a duty to preserve marriage and family as established by God. The time has now come when a constitutional amendment is needed in this country to protect our divine inheritance. Such action does not reduce our regard for individuals who choose to live by other standards. But it confirms our conviction that marriage is the foundry for social order, the fountain of virtue and the foundation for eternal exaltation.
In September 2019, he spoke to students at Brigham Young University on five truths, one of which addressed the position of the Church on marriage.
Thus our commission as apostles is to teach nothing but truth. That commission does not give us the authority to modify divine law.Though we of the First Presidency and Quorum of the Twelve Apostles cannot change the laws of God, we do have the charge “to build up the church, and regulate all the affairs of the same in all nations.” Thus we can adjust policy when the Lord directs us to do so. You have recently seen such examples. Because the Restoration is ongoing, policy changes will surely continue.
For example, let’s consider the definition of marriage. In recent years, many countries, including the United States, have legalized same-sex marriage. As members of the Church, we respect the laws of the land and abide by them, including civil marriage. The truth is, however, that in the beginning—in the beginning—marriage was ordained by God! And to this day it is defined by Him as being between a man and a woman. God has not changed His definition of marriage.
God has also not changed His law of chastity. Requirements to enter the temple have not changed. And our desire for there to be love at home and harmony between parent and child has not changed.
- In California in 2000, Proposition 22, banning same-sex marriage, was passed by 61% of voting Californians and was openly supported by the Church.
- In Utah, in 2004, Amendment 3 to the state constitution was passed by 66% of those voting.
- In 2006 the Church joined with other religious leaders to show support for an amendment to the US Constitution defining marriage as being between a man and a woman.
- In 2008, the Church joined a coalition to support Proposition 8, which amended the California constitution to define marriage as being between a man and a woman. The law created by Proposition 22 had been overturned by the California Supreme Court.
- In November, 2009, citizens of the State of Maine overturned the state legislature's decision to allow gay marriage. Gay marriage has now lost in every single state — 31 in all — in which it has been put to a popular vote. Gays had hoped for success in Maine, since New England has been the most liberal region in the U.S. regarding gay marriage. The outcome marked the first time voters had rejected a gay-marriage law enacted by a legislature. When Californians put a stop to same-sex marriage a year ago, it was in response to a court ruling, not legislation. Five other states have legalized gay marriage —starting with Massachusetts in 2004, and followed by Vermont, New Hampshire, Connecticut and Iowa — but all did so through legislation or court rulings, not by popular vote. In contrast, constitutional amendments banning gay marriage have been approved in all 30 states where they have been on the ballot.
- Following the Maine referendum, the New York legislature decided to reject a bill legalizing gay marriage. "This is an enormous victory," said Maggie Gallagher, the leader of the anti-gay marriage group, National Organization for Marriage. "What you saw was the will of the people. ... The culture really hasn't shifted on gay marriage."
- New York is one of the most politically liberal states in the country. Recent polls showed a majority of New York voters favor allowing same-sex couples to marry, but one poll showed the public evenly split. 
- Washington, D.C.'s City Council voted to allow same-sex marriage in December, 2009. Congress likely will not weigh in on the bill, which usually would require congressional approval. Standing aside keeps the bill from becoming a referendum on gay marriage. Opponents included the [Catholic] Archdiocese of Washington, which said it might have to stop providing adoptions and other services because the law would force it to extend benefits to same-sex couples. 
These types of political situations continued until finally the courts decided to make gay marriage legal throughout the United States. As of October 2019, 30 countries worldwide legalized same-sex marriages. The Church continued to promote traditional marriage in other countries where decisions were still being made.
Chastity outside of marriage, with marriage being a sacred covenant is central to church doctrine. Fidelity inside marriage is also central, and members of the Church believe children do best with biological parents in a stable, long-term relationship. The Church will not change its doctrines according to modern social mores of the world, even though many think it should. As President Nelson noted, "leaders of the Church are criticized for holding firm to the laws of God, defending the Savior’s doctrine, and resisting the social pressures of our day." However, "because the Restoration is ongoing, policy changes will surely continue." One was changing gay marriage entered into by members of the Church as "apostasy," meaning turning against doctrine. It is still considered a serious transgression. Although disciplinary processes are the same, making gay marriage a sin against doctrine protects the Church legally in a society that sees no sexual sin, only intolerance.
- Gay Mormons
- The Church's response to gay civil rights legislation in Utah
- A definitive article on same sex marriage
- Gay Marriage, Democracy, and the Courts from Wall Street Journal
- Religious Coalition for Marriage
- Protect Marriage Coalition
- Mormon.org - Homosexuality
- Marriage Matters to Kids
- Preserving the Divine Institution of Marriage - An official Latter-day Saint site in support of California Proposition 8 in 2008.
- Judge Walker overturns Prop 8
- Prop 8 appeals will end up in US Supreme Court
- Policy Changes Announced for Members in Gay Marriages, Children of LGBT Parents
- What is the difference between doctrine and policy?