a group of persons united by the ties of marriage, blood, or adoption, constituting a single household and interacting with each other in their respective social (sociology) positions, usually those of spouses, parents (parent), children (childhood), and siblings. The family group should be distinguished from a household, which may include boarders and roomers sharing a common residence. It should also be differentiated from a kindred (which also concerns blood lines), because a kindred may be divided into several households. Frequently the family is not differentiated from the marriage pair, but the essence of the family group is the parent-child relationship, which may be absent from many marriage pairs.

At its most basic, then, a family consists of an adult and his or her offspring. Most commonly, it consists of two married adults, usually a man and a woman (almost always from different lineages and not related by blood) along with their offspring, usually living in a private and separate dwelling. This type of unit, more specifically known as a nuclear family, is believed to be the oldest of the various types of families in existence. Sometimes the family includes not only the parents and their unmarried children living at home but also children that have married, their spouses, and their offspring, and possibly elderly dependents as well; such an arrangement is called an extended family.

At its best, the family performs various valuable functions for its members. Perhaps most important of all, it provides for emotional and psychological security, particularly through the warmth, love, and companionship that living together generates between spouses and in turn between them and their children. The family also provides a valuable social and political function by institutionalizing procreation and by providing guidelines for the regulation of sexual conduct. The family additionally provides such other socially beneficial functions as the rearing and socialization of children, along with such humanitarian activities as caring for its members when they are sick or disabled. On the economic side, the family provides food, shelter, clothing, and physical security for its members, some of whom may be too young or too old to provide for the basic necessities of life themselves. Finally, on the social side, the family may serve to promote order and stability within society as a whole.

Historically, in most cultures, the family was patriarchal (patriarchy), or male-dominated. Perhaps the most striking example of the male-dominated family is the description of the family given in the Hebrew Bible (or Old Testament), where the male heads of the clans were allowed to have several wives as well as concubines. As a general rule, women had a rather low status. In Roman (ancient Rome) times the family was still patriarchal, but polygamy was not practiced, and in general the status of women was somewhat improved over that suggested in the Hebrew Bible, although they still were not allowed to manage their own affairs. The Roman family was an extended one. The family as it existed in medieval Europe was male-dominated and extended.

In the West, industrialization (Industrial Revolution) and the accompanying urbanization spawned—and continue to spawn—many changes in family structure by causing a sharp change in life and occupational styles. Many people, particularly unmarried youths, left farms and went to urban centres to become industrial workers. This process led to the dissolution of many extended families.

The modern family that emerged after the Industrial Revolution is different from the earlier model. For instance, patriarchal rule began to give way to greater equality between the sexes. Similarly, family roles once considered exclusively male or female broke down. Caring for the home and children, once the exclusive duty of the female, is often a shared activity, as, increasingly, is the earning of wages and the pursuit of public life, once the exclusive domain of the male. The structure of the family is also changing in that some couples choose not to marry legally and instead elect to have their children out of wedlock; many of these informal relationships tend to be of short duration, and this—as well as the rise in levels of divorce—has led to a rapid increase in the number of one-parent households.

Especially in Western cultures, the modern family is today more of a consuming as opposed to a producing unit, and the members of the family work away from home rather than at home. Public authorities, primarily governmental ones, have assumed many of the functions that the family used to provide, such as caring for the aged and the sick, educating the young, and providing for recreation. Technological advancements have made it possible for couples to decide if and when they want to have children.

Family law varies from culture to culture, but in its broadest application it defines the legal relationships among family members as well as the relationships between families and society at large. Some of the important questions dealt with in family law include the terms and parameters of marriage, the status of children, and the succession of property from one generation to the next. In nearly every case, family law represents a delicate balance between the interests of society and the protection of individual rights.

The general rule in marriages until modern times was the legal transfer of dependency, that of the bride, from father to groom. Not only did the groom assume guardianship, he usually assumed control over all of his wife's affairs. Often, the woman lost any legal identity through marriage, as was the case in English common law. There have been exceptions to this practice. Muslim women, for instance, had considerable control over their own personal property. The use of dowries (dowry), an amount of money or property given to the husband with the bride in compensation for her dependency, has long been practiced in many countries, but it has tended to disappear in many industrial societies.

In general, modern marriage is best-described as a voluntary union, usually between a man and a woman (although there are still vestiges of the arranged marriage that once flourished in eastern Europe and Asia). The emancipation of women in the 19th and 20th centuries changed marriage dramatically, particularly in connection with property and economic status. By the mid-20th century, most Western countries had enacted legislation establishing equality between spouses. Similarly changed is the concept of economic maintenance, which traditionally fell on the shoulders of the husband. Though many laws still lean toward this view, there was increasing recognition of a woman's potential to contribute to the support of the family. At the beginning of the 21st century, family law and the notion of family itself was further complicated by calls for acceptance of same-sex marriages and nontraditional families.

Dissolution of marriages is one of the areas in which laws must try to balance private and public interest, since realistically it is the couple itself that can best decide whether its marriage is viable. In many older systems—e.g., Roman, Muslim, Jewish, Chinese, and Japanese—some form of unilateral divorce was possible, requiring only one party to give notice of the intention, usually the male. Most modern systems recognize a mutual request for divorce, though many require an attempt to reconcile before granting divorce. Extreme circumstances, in which blatant neglect, abuse, misbehaviour, or incapacity can be demonstrated, find resolution in civil court. Many systems favour special family courts that attempt to deal more fairly with sensitive issues such as custody of children.

The issue of children poses special problems for family law. In nearly every culture, the welfare of children was formerly left to the parents entirely, and this usually meant the father. Most societies have come to recognize the general benefit of protecting children's rights and of prescribing certain standards of rearing. Thus, more than in any other area, family law intervenes in private lives with regard to children. Compulsory education is an example of the law superseding parental authority. In the case of single-parent homes, the law will frequently provide some form of support. Legislation on child labour and child abuse also asserts society's responsibility for a child's best interests.

The succession (inheritance) of family interests upon the death of its members can be considered a part of family law. Most legal systems have some means of dealing with division of property left by a deceased family member. The will, or testament, specifies the decedent's wishes as to such distribution, but a surviving spouse or offspring may contest what appear to be unreasonable or inequitable provisions. There are also laws that recognize family claims in the event that property is left intestate (i.e., with no will to determine its distribution).