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 Colorado, incest is defined as a sexual relationship between relatives who are not legally permitted to marry. The Colorado Revised Statutes (C.R.S. 18-6-301) specifically prohibit sexual relations between a parent and child, a grandparent and grandchild, and between siblings, whether by the whole or half blood or by adoption. This law also extends to any children of a sibling as well as relations between an aunt or uncle with a niece or nephew. Incest in Colorado is considered a class 4 felony, which can result in serious legal consequences, including imprisonment. Consent is not a defense to a charge of incest in Colorado, meaning that the crime can be prosecuted even if both parties were willing participants in the sexual act.