Incest is marriage or sexual relations between close relatives. The criminal offense of incest may also be known as prohibited sexual conduct. Laws vary from state to state, but incest laws generally prohibit marriage or sexual relations between (1) a person’s ancestor or descendant by blood or adoption; (2) a person’s current or former stepchild or stepparent; (3) a person’s parent’s brother or sister of the whole or half blood; (4) a person’s brother or sister of the whole or half blood or by adoption; (5) the children of a person’s brother or sister of the whole or half blood, or by adoption; or (6) the son or daughter of a person’s aunt or uncle of the whole or half blood or by adoption.

Lack of consent to sexual relations between such relatives is not an element of the crime, and persons may be guilty of the crime even if both parties consented.

Laws regarding incest or prohibited sexual contact vary from state to state and are generally located in a state’s statutes—often in the penal or criminal code. The crime is a felony offense in many states, with potential punishment of significant jail or prison time.

In Washington State, incest is defined as sexual intercourse between persons who are closely related, and it is considered a criminal offense. Specifically, under Washington law, incest includes sexual relations between a person and his or her parent, sibling, child, grandchild, uncle, aunt, nephew, or niece. This applies to both blood relations and those relations created by marriage, such as stepchildren or stepparents. Incest is classified as a Class C felony in Washington, which can result in serious legal consequences, including imprisonment. Consent is not a defense to a charge of incest, meaning that even if both parties agree to the sexual relationship, they can still be prosecuted under the law. The relevant statutes can be found in the Revised Code of Washington (RCW), particularly in the criminal code.