In the English common law tradition, from which our legal doctrines and concepts have developed, a marriage was a contract based upon a voluntary private agreement by a man and a woman to become husband and wife. Marriage was viewed as the basis of the family unit and vital to the preservation of morals and civilization. Traditionally, the husband had a duty to provide a safe house, pay for necessities such as food and clothing, and live in the house. The wife's obligations were maintaining a home, living in the home, having sexual relations with her husband, and rearing the couple's children. Today the underlying concept that marriage is a legal contract still remains but due to changes in society the legal obligations are not the same.

Marriage is chiefly regulated by the states. The Supreme Court has held that states are permitted to reasonably regulate the institution by prescribing who is allowed to marry, and how the marriage can be dissolved. Entering into a marriage changes the legal status of both parties and gives both husband and wife new rights and obligations. One power that the states do not have, however, is that of prohibiting marriage in the absence of a valid reason. For example, prohibiting interracial marriage is not allowed for lack of a valid reason and because it was deemed to violate the Equal Protection Clause of the Constitution.

All states limit people to one living husband or wife at a time and will not issue marriage licenses to anyone with a living spouse. Once an individual is married, the person must be legally released from the relationship by either death, divorce, or annulment before he or she may remarry. Other limitations on individuals include age and close relationship. Limitations that some but not all states prescribe are: the requirements of blood tests, good mental capacity, and being of opposite sex.

In 1996, President Clinton signed into law the Defense of Marriage Act (DOMA) (http://thomas.loc.gov/cgi-bin/query/z?c104:H.R.3396:), which, for federal purposes, defined marraige as "only a legal union between one man and one woman as husband and wife" (1 U.S.C. § 7). DOMA further provided that "No State, territory, or possession of the United States, or Indian tribe, shall be required to give effect to any public act, record, or judicial proceeding of any other State, territory, possession, or tribe respecting a relationship between persons of the same sex that is treated as a marriage under the laws of such other State, territory, possession, or tribe, or a right or claim arising from such relationship" (28 U.S.C. § 1738C).