A person's mother-in-law is the mother of his or her spouse. A person is a son-in-law or daughter-in-law to the mother-in-law. She and the father-in-law are the parents of the spouse and, in a nuclear family, of the sisters-in-law and brothers-in-law. Together the members of this family affinity group are called the in-laws.

In comedies, the mother-in-law is sometimes shown as the bane of the husband, who is married to the mother-in-law's daughter. Mothers-in-law are often stereotyped in mother-in-law jokes.

Some Australian Aboriginal languages use avoidance speech, so-called "mother-in-law languages", special sub-languages used when in hearing distance of taboo relatives, most commonly the mother-in-law.

A Mother-in-law suite is also a type of dwelling, usually guest accommodations within a family home that may be used for members of the extended family.

See also

• affinity (law)