The nuclear family or elementary family is a term used to define a family group consisting of a pair of adults and their children. This is in contrast to a single-parent family, to the larger extended family, and to a family with more than two parents. Nuclear families typically center on a married couple; the nuclear family may have any number of children. There are differences in definition among observers; some definitions allow only biological children that are full-blood siblings, while others allow for a stepparent and any mix of dependent children including stepchildren and adopted children.
The traditional definition of a nuclear family is a family unit that includes two married parents of opposite genders and their biological or adopted children living in the same residence. However, the term "nuclear family" can mean several different things in today's society. Understanding the classic roles in this type of family and how it is defined can help you understand the relationships in your own family, whether it's nuclear or not.
Family structures of one married couple and their children were present in Western Europe and New England in the 17th century, influenced by church and theocratic governments. With the emergence of proto-industrialization and early capitalism, the nuclear family became a financially viable social unit. The term nuclear family first appeared in the early twentieth century. Alternative definitions have evolved to include family units headed by same-sex parents, and perhaps additional adult relatives who take on a cohabiting parental role; in this latter case it also receives the name of conjugal family.
The concept that a narrowly defined nuclear family is central to stability in modern society has been promoted by familialists who are social conservatives in the United States, and has been challenged as historically and sociologically inadequate to describe the complexity of actual family relations.