There must be a showing by the prosecutor that the accused party and another named party had sexual relations.Depending on state statutes, the prosecutor must show that either one or both parties to the adultery were wed to someone else at the time of their relationship. Other statutes provide that the act is criminal only if the woman is married.Under the law of many states, a single act of adultery constitutes a crime, whereas in others, there must be an ongoing and notorious relationship.The court also noted that the fear of prosecution prevents infected people from voluntarily seeking treatment. Finally, judges, prosecutors, and other state officials have increasingly realized that prosecutions for adultery have had little practical effect in "safeguarding the community morals." Opinion polls consistently show that significant numbers of spouses admit to cheating on their partners during marriage. In light of the growing evidence that adultery laws no longer serve their three underlying purposes, most state prosecutors have made a conscious decision against wasting their scarce resources on prosecuting alleged adulterers. In states that still have adultery laws on the books, but have failed to prosecute anyone under them recently, courts have ruled that the mere lack of prosecution under the adultery statute does not result in that statute becoming invalid or judicially unenforceable. Occasionally, adultery has been successfully asserted as a defense to the crime of murder by an individual charged with killing his or her spouse's lover. Courts have also rejected the argument that prosecutions for adultery are inconsistent with the right to privacy guaranteed by state and federal constitutions. Courts are loath, however, to excuse the heinous crime of murder on the ground that the accused party was agitated about a spouse's adulterous activities.
Under some statutes, both parties to an adulterous relationship are guilty of a crime if either of them is married to someone else.
In such states, a complaint can be filed by a husband or wife against the adulterous spouse's lover.
Evidence Customary rules prescribe the types of evidence that can be offered to prove guilt or innocence.
In Europe during the fifteenth and sixteenth centuries, adultery was punishable solely in courts created by the church to impose good morals.
In the ecclesiastical courts, adultery was any act of sexual intercourse by a married person with someone not his or her spouse.
In a few jurisdictions only the married party can be prosecuted for adultery.