The ancient practice of polygamy became prevalent in parts of the United States in the mid-nineteenth century, when the Mormon Church canonized the doctrine of polygamy and encouraged its practice among its members. Today, there are nearly 40, 000 polygamists in the United States, mostly living in Utah. The Supreme Court has ruled on polygamy several times in decisions and dicta, each time finding it to be unconstitutional within the United States. In Reynolds v. United States, a 1878 decision upholding a statute that criminalized polygamy, the Court introduced the belief/action distinction that controls religious First Amendment doctrine today. This Note discusses the history of religious polygamy and argues that the Court should reexamine its previous rulings and should declare the practice of religious polygamy constitutional under the Free Exercise Clause of the First Amendment and the right to privacy within a marriage.