母系制度，是以母系亲属为世系继承的亲属制度。

采取母系制度的社会通常有母系继承制、从妻居、重视舅甥关系、从母居以及母亲担任家长的情况。在母系社会中，原生家庭的子嗣被严格归类为母系亲属的成员，继承母系的姓氏、财产，并共同祭祀母系的祖先。

值得注意的是，母系制度系指涉子嗣对母方家族的严格继承，并非是父系制度的相对概念。与常见的误解不同，母性制度不必然产生女权高于男权的情况。实际上，母系社会常见的情况是，男性的权力集中在公共事务上，女性的权力则主要在家庭内的事务上。男性成员通常成长于父系与母系家族之间，然而在母系的家族时，才有实质的身分和发言权。因为这样，舅舅通常扮演监护人角色，而且成为氏族的实质领袖。

Matrilineality is the tracing of descent through the female line. It may also correlate with a societal system in which each person is identified with their matriline – their mother's lineage – and which can involve the inheritance of property and/or titles. A matriline is a line of descent from a female ancestor to a descendant (of either sex) in which the individuals in all intervening generations are mothers –in other words, a "mother line". In a matrilineal descent system, an individual is considered to belong to the same descent group as her or his mother. This matrilineal descent pattern is in contrast to the more common pattern of patrilineal descent from which a family name is usually derived. The matriline of historical nobility was also called her or his enatic or uterine ancestry (corresponding to the patrilineal "agnatic" ancestry).