姻亲指基于婚姻关系而生之亲属型态。包括配偶的血亲、血亲的配偶、配偶的血亲的配偶。

在父系社会，已婚女性被视为夫家的成员，与姻亲（婆家）会有较为紧密的联系，有时甚至超过自己的原生家庭（娘家），例如与丈夫的父母（家翁、家姑）以及丈夫的兄弟、未婚姊妹以及丈夫兄弟的妻子（妯娌）同住，平时也要照顾翁姑和丈夫的未婚兄弟姊妹。即使与丈夫另外组织核心家庭，传统上媳妇也常要探望翁姑并帮忙做家事。男性与妻家的关系通常较自己的原生家庭疏离，虽然对妻子的父母（岳丈、岳母）也要有一定的照顾，但传统上只需要抽空探望，到妻子娘家通常也会被视为客人。

In law and in cultural anthropology, affinity, as distinguished from consanguinity (blood relationship), is the kinship relationship that is created or exists between two or more people as a result of somebody's marriage. It is the relationship which each party to a marriage has to the relations of the other partner to the marriage; but does not cover the marital relationship of the parties to the marriage themselves. Though laws vary considerably, affinity does not always cease with the death of one of the marriage partners through whom affinity is traced, nor with the divorce of the marriage partners. In addition to kinship by marriage, "affinity" can sometimes also include kinship by adoption and step relationship.