Families consist of bonds of kin and marriage and make up a major organizing institution of society. Kinship describes the social bonds that unite individuals into families.

There are three main forms of kinship: bloodline, marriage, and adoption. In most societies, the institution of family creates a social group in which to procreate, rear children, pass on cultural knowledge, and cooperate to better meet life’s challenges. In the United States’ recent history, the most common concept of family has been one man and one woman living together with their children. This structure is known as the nuclear family. However, other groups of related individuals or families are possible.

Diversity in family forms can manifest in many ways. Two heterosexual parents might be considered a traditional form, but there has always been diversity in family structure, including one-parent families, couples that have no children, and gay and lesbian families. In many places, multiple generations of a family will dwell together in an extended family model. Other family types include polygyny (more than one woman married to a man) and polyandry (more than one man married to a woman). The term polygamy encompasses both of these possibilities. American ideas about family are shifting. Rising rates of divorce, blended families, single-parenting, unmarried cohabitation, and same-sex marriage are leading to a more inclusive idea of what constitutes a family.

When families are a source of financial and emotional support for many people, for the family can be dangerous. Violence in the family comes in many forms and includes emotional, physical, or sexual abuse. Victims of violence are usually non-dominant members of the family such as elders, females, or children. It is important to remember that males can be victims of domestic violence. Victims may find it difficult to leave their abusers due to dependence on the family for resources. The risk of family violence increases with some types of substance abuse, particularly alcohol.