One of the requirements to reach 'exaltation' -- the fullness of all that God has to offer -- is what Mormons call "celestial marriage."

Celestial marriage is a marriage in a Mormon temple designed to last not just until death but throughout all eternity. It is not a practice taught or condoned by historic, Biblical Christianity

Read the full article: Celestial Marriage at Apologetics Index

How the Mormon Church outlawed polygamy, "The Most Holy And Important Doctrine Ever Revealed."

Read the full article: Polygamy in Mormonism at Apologetics Index