The legal definition of adultery is voluntary sexual intercourse between a married person and someone who is not their spouse. Two things have to be true at once: at least one participant must be legally married at the time, and the encounter must be voluntary on both sides. Forced or coerced contact belongs to entirely different areas of law. That core meaning has held steady across centuries; what has changed, and changed a lot, is what happens when adultery is proven.
What Counts as Sexual Intercourse
Traditionally, courts read “sexual intercourse” narrowly, as vaginal penetration. Under that reading, emotional affairs, flirtation, and physical intimacy short of intercourse do not qualify. That narrow framing is still the default in most states.
Two shifts are worth knowing about. The military expanded its definition in 2019 to cover oral and anal sexual contact and same-sex conduct. Some state courts have moved in a similar direction for divorce purposes, recognizing a wider range of sexual activity as adultery. But the intercourse-only standard remains the more common one in state family law.
Adultery in Divorce
Most states still allow a spouse to file for divorce on fault-based grounds, and adultery is the most commonly cited fault ground. Filing on fault can matter because it sometimes influences how a court divides property, awards alimony, or both. In practice, most divorces still proceed under no-fault provisions because they move faster and generate less conflict.
Dissipation of Marital Assets
Even in no-fault states, adultery can change the financial outcome when marital money was spent on the affair. Courts call this dissipation of marital assets. If one spouse used joint funds on hotel rooms, gifts, trips, or rent for a paramour, the other spouse can ask the court to account for that spending. The claimant has to show the money was spent during the breakdown of the marriage and served no legitimate marital purpose. Courts that agree typically adjust the property split to compensate the non-offending spouse for the wasted funds. There is no set dollar threshold; reported dissipation amounts have ranged from a few hundred dollars to hundreds of thousands, depending on the size of the estate.
Alimony
The effect on spousal support varies widely by state. Georgia statutorily bars an adulterous spouse who caused the end of the marriage from receiving alimony. Other states treat adultery as one factor among many that a judge may weigh, without making it an automatic disqualifier. In pure no-fault jurisdictions, courts generally cannot consider marital misconduct when setting alimony at all, though dissipation claims can still shift the numbers indirectly by changing how much of the marital estate each spouse walks away with.
Is Adultery a Crime
Adultery is still a criminal offense in roughly 16 states with clearly defined statutes, plus a further group of states that never formally repealed older laws. Three states classify it as a felony: Michigan, Oklahoma, and Wisconsin. The rest treat it as a misdemeanor, with penalties that can include fines and short jail sentences. Virginia, for example, classifies it as a Class 4 misdemeanor.
Prosecutions are extraordinarily rare. The trend over the past several decades has been steady repeal. Minnesota removed adultery from its criminal code in 2023, following a broader pattern of states concluding that criminal law is not the right tool for policing marital fidelity. The statutes that remain are widely viewed as relics, and enforcement is essentially nonexistent in most jurisdictions.
The constitutional status of these laws is unsettled. The Supreme Court’s 2003 decision in Lawrence v. Texas held that intimate consensual sexual conduct is protected by the Due Process Clause of the Fourteenth Amendment. The Ninth Circuit has applied that reasoning to conclude that adultery is constitutionally protected conduct. The Fifth and Tenth Circuits have taken a narrower view. No Supreme Court case has directly addressed whether criminal adultery statutes survive Lawrence. As a practical matter, the ambiguity rarely matters because almost no prosecutor brings these charges.
Adultery in the Military
The U.S. military is the one institution that still actively prosecutes extramarital sexual conduct. In 2019, the offense was renamed from “adultery” to “extramarital sexual conduct” under Article 134 of the Uniform Code of Military Justice. The new definition covers a broader range of sexual activity, including oral and anal contact and same-sex conduct, not just traditional intercourse.
A conviction requires the government to prove three elements: that the service member engaged in extramarital sexual conduct, that the accused knew at the time that they or the other person was married to someone else, and that the conduct was prejudicial to good order and discipline or of a nature to bring discredit upon the service.1United States Court of Appeals for the Armed Forces. Core Criminal Law Subjects: Crimes: Article 134 – Adultery
That third element is where the real analysis happens. The military does not punish extramarital sex simply because it occurred. Prosecutors must show it harmed the professional environment. Factors that courts-martial weigh include the rank of the accused, whether the other person was also a service member, the impact on unit morale, and whether the accused attempted to conceal the relationship. A discreet relationship between two people in different commands with no operational overlap is far less likely to draw charges than an affair between an officer and an enlisted member’s spouse in the same unit.1United States Court of Appeals for the Armed Forces. Core Criminal Law Subjects: Crimes: Article 134 – Adultery
Civil Suits Against the Third Party
A small number of states let the non-cheating spouse sue the person their partner had an affair with. These claims take two forms, and the states that recognize them do not always recognize both.
- Criminal conversation. A tort that allows a spouse to sue a third party for having sexual intercourse with their husband or wife. The claim does not require proof that the third party caused the marriage to fail, only that the sexual relationship occurred. As of 2024, roughly seven states still recognize this claim: Hawaii, Illinois, Mississippi, New Mexico, North Carolina, South Dakota, and Utah.
- Alienation of affection. A broader tort targeting conduct that destroyed the marital relationship, which can include but is not limited to a sexual affair. The plaintiff must show genuine love and affection between the spouses, that the defendant’s conduct destroyed it, and that the defendant’s actions were a proximate cause of the loss. Roughly five or six states still allow these suits, with heavy overlap with the criminal conversation list.
Damages can be substantial: compensation for emotional distress, humiliation, loss of companionship, and loss of financial support, along with punitive damages in many jurisdictions that still recognize the claims. North Carolina has produced some of the largest known awards, with juries occasionally reaching seven-figure verdicts. Collection is a separate problem; a large verdict means little if the defendant lacks assets.
Effect on Child Custody
Adultery by itself rarely changes a custody outcome. Courts decide custody based on the best interests of the child, and a parent’s sexual behavior outside the marriage generally does not bear on their ability to parent. A judge is not going to transfer custody because one parent had an affair.
The exceptions involve cases where the affair directly affected the children: exposure to instability, neglect, or an unsafe environment, or a parent who routinely left young children unsupervised to spend time with a paramour. In those cases, infidelity becomes relevant not as a moral failing but as evidence of impaired parenting.
How Adultery Gets Proven
Direct evidence is rare for obvious reasons. Courts have long relied on a circumstantial standard known as the inclination and opportunity test. If the accusing spouse can show both that the other spouse had a romantic or sexual desire for a specific person and that the two had a realistic chance to act on it, a court can infer the affair.
Inclination is the easier element in the age of digital communication. Text messages, emails, direct messages on social media, and photos that reveal a romantic or sexual relationship all serve as evidence of intent. Public displays of affection witnessed by friends, coworkers, or family members work too. The goal is to show the court that the relationship was more than friendship.
Opportunity means proving the two people were alone together in circumstances where the affair could have occurred. Hotel receipts, travel records, credit card statements for flights or rideshare trips, and evidence of overnight stays all support this element. A spouse who can show that their partner regularly visited someone’s private residence during unexplained absences is building an opportunity case.
When both elements come together through credible evidence, the court draws the inference. The standard of proof in divorce proceedings is a preponderance of the evidence, meaning it is more likely than not that the affair occurred. That is a significantly lower bar than the beyond a reasonable doubt standard used in criminal cases.
One caution on gathering evidence yourself. Accessing a partner’s email, phone, or social media accounts without permission can violate federal wiretapping or computer fraud laws, even between spouses. Evidence obtained that way may be excluded and could expose the snooping spouse to separate legal liability. The safer path is to preserve evidence you already have legitimate access to and let an attorney advise on what further investigation is permissible in your jurisdiction.