Polygamy

Polygamy is a word that comes from late Greek. It can be translated as "many marriages". It refers to any form of marriage where a person has "more than one spouse". There is also a concept called group marriage. In group marriage, all the (adult) members of the group are responsible for all the children.
A man being married to more than one woman at the same time is called polygyny. A woman being married to more than one man at the same time is called polyandry. 
Both forms have occurred in humans. Polygyny is much more common, and is practised by millions of people, mostly in Muslim and African countries. According to Muslim 
Sharia law, a man can have many wives at the same time. In many African Pagan religions, polygamy is a common custom, and there is often no limit to the number of women a man can marry. In most non-Muslim and non-African countries, polygamy is illegal, and a person who has more than one spouse can be prosecuted for bigamy. Some countries, including India, only permit Muslims to be polygamous.
The Church of Jesus Christ of Latter-day Saints.
Polygamy is one of the beliefs of Mormon Fundamentalists. These are Mormons (members of The Church of Jesus Christ of Latter-day Saints) who strictly follow the teachings of Joseph Smith. Smith felt it was his job to restore plural marriage to the earth. He was married to 33 women. In 1890 the Mormon church officially stopped "celestial marriages" (polygamy). Church members who continue to practice plural marriage are excommunicated from the church.
Sethepu/Isithembu.
Isithembu (Sethepu) is the African practice of a man being able to have more than one wife at the same time. A man may marry again if his current wife or wives cannot have children. He keeps his current wife or wives as divorce is not allowed. A man may marry again if his current wife or wives have not produced male children. He can marry again if a wife does not want children. In some places, if a man dies, his wife or wives are married to his brother. This way his family is cared for. The Swazi culture says a man should have many wives. Polygamy (Isithembu) is normal for men. Woman should have children, which is normal for them.