Under civil law, Nigeria does not recognize polygamous unions. However, 12 out of the 36 Nigerian states recognize polygamous marriages as being equivalent to monogamous marriages. All twelve states are governed by Sharia law. The states, which are all northern, include the states of Bauchi, Borno, Gombe, Jigawa, Kaduna, Kano, Katsina, Kebbi, Niger, Sokoto, Yobe, and Zamfara, which allow men to take more than one wife.

Nigeria is part of the "polygamy belt", a region in West Africa and Central Africa where polygamy is common and deeply rooted in the culture. Nigeria is estimated to have the fifth highest polygamy prevalence in the world, with 28% of the population living in polygamous marriages, with only four countries (Burkina Faso, Mali, Gambia and Niger) having a higher prevalence.

Zamfara State was the first to legislate polygamy, which occurred on January 7, 2000. Gombe State has been the most recent state to provide for civil polygamy, legalizing it on December 14, 2001.

As the southern region of Nigeria is predominantly Christian, polygamous marriages have not been legally introduced at this time. Attempts to introduce Sharia (thereby legalizing polygamy) have been made in Oyo State, Kwara State, Lagos State, and several others, but all have been unsuccessful. Polygamous unions are recognized by customary law in Nigeria, providing a handful of benefits for those in polygamous unions ranging from inheritance rights to child custody.

As of 2009, there has yet to be any debate of introducing a measure that would allow for civil polygamous marriages to be recognized nationwide, rather than allowing legislation to remain on a state-by-state basis. There are an estimated forty million polygamists in Nigeria.

There are no requirements based on religion in the North, therefore Christians are legally allowed to form polygamous unions just as Muslims may do. Christian church leaders such as Archbishop Peter Akinola of the Anglican Church of Nigeria have condemned the practice of polygamy by Christians, with Akinola going on to write "The observation [of polygamy] will destroy our witness if not firmly addressed. We cannot claim to be a Bible-believing church and yet be selective in our obedience." Reports of Nigerian Mormons practicing polygamy have also surfaced.

Despite the four-wife limitation, there have been numerous indications that many Nigerians bypass this law, such as with Muhammadu Bello Masaba, an 84-year-old Islamic cleric who was accused of illegal marriage due to his exceeding number of spouses, in which he had 86 wives. The charges were later withdrawn by the Niger State Sharia commission, with Masaba able to retain all of his spouses.

On an opposite note, it was reported in April 2007 that a Nigerian lesbian, Aunty Maiduguri, married four women in an elaborate ceremony in Kano State, though her union is not recognized by the government, and Maiduguri and her partners were forced to go into hiding shortly after the ceremony to avoid the possible threat of being stoned if convicted for lesbianism, which results in capital punishment for married Muslim women or caning for single Muslim women in Nigerian areas under Sharia law.