夫兄弟婚，也称利未婚、转房婚，是指女性在丈夫死后嫁给其兄弟的行为、习俗或法律。广义的转房婚也包括改嫁给夫家其他男性，例如亡夫的叔、伯、儿子（女方的亲生子除外）、侄、甥等的情况。夫死后嫁给丈夫儿子的婚姻又称收继婚。多数社会都存在有夫兄弟婚的实际行为。但社会对此类婚姻的态度可分为反对、中立、支持鼓励、甚至被认为是义务。其实是原始社会的群婚制度。（在江苏省与河南汉族也有，有人说是开封犹太人风俗）

由于这样的男女双方本来就认识甚至熟悉，其结婚可能是个人选择。有的是出于经济考虑。贫困人家娶寡嫂、弟媳等，解决了赡养她们的问题，也省了聘礼。如果寡妇继承了财产，这样的婚姻可以防止家庭财富外流。社会视女性为夫家财产的时候，夫兄弟婚也可被理解为一种继承。另外政治也可成为夫兄弟婚的动机。例如英国的亨利八世娶其寡嫂凯瑟琳，目的是加强英国和西班牙王室的联盟。

Levirate marriage is a type of marriage in which the brother of a deceased man is obliged to marry his brother's widow, and the widow is obliged to marry her deceased husband's brother.

Levirate marriage has been practiced by societies with a strong clan structure in which exogamous marriage (i.e. marriage outside the clan) was forbidden. It has been known in many societies around the world. The practice is similar to widow inheritance, where, for example, the deceased husband's kin can dictate whom the widow may marry.