Polygamy  is the practice of marrying multiple spouses. When a man is married to more than one wife at a time, sociologists call this polygyny. When a woman is married to more than one husband at a time, it is called polyandry. If a marriage includes multiple husbands and wives, it can be called a group marriage.

In contrast, monogamy is marriage consisting of only two parties. Like "monogamy", the term "polygamy" is often used in a de facto sense, applied regardless of whether the state recognizes the relationship. In sociobiology and zoology, researchers use polygamy in a broad sense to mean any form of multiple mating.

Worldwide, different societies variously encourage, accept or outlaw polygamy. Of societies which allow or tolerate polygamy, in the vast majority of cases the form accepted is polygyny. According to the Ethnographic Atlas (1998), of 1,231 societies noted, 588 had frequent polygyny, 453 had occasional polygyny, 186 were monogamous and 4 had polyandry;^[ although more recent research suggests polyandry may be more common than previously thought. In cultures which practice polygamy, its prevalence among that population is often connected to class and socioeconomic status.

From a legal point of view, in many countries, although marriage is legally monogamous (a person can only have one spouse, and bigamy is illegal), adultery is not illegal, leading to a situation of de facto polygamy being allowed, although without legal recognition for non-official "spouses".

According to scientific studies, the human mating system is considered to be primarily monogamous, with cultural practice of polygamy to be in the minority, based on both surveys of world populations, and on characteristics of human reproductive physiology.