Adultery is voluntary sexual intercourse between a married person and one who is not his or her spouse. Some legal jurisdictions have defined it as "crime against marriage", (Germany: § 1353 Abs. 1 S. 2 BGB) as opposed to infidelity.
Although the definition of "adultery" differs in nearly every legal system, the common theme is sexual relations outside of marriage, in one form or another.
North Carolina defines adultery as when any man and woman "lewdly and lasciviously associate, bed and cohabit together." (North Carolina Statute 14-184 
Minnesota defines adultery as: "when a married woman has sexual intercourse with a man other than her husband, whether married or not, both are guilty of adultery". (Minnesota Statute section 609.36 
Adultery was known in earlier times by the legalistic term "criminal conversation" (another term, alienation of affection, is used when one spouse deserts the other for a third person). The term originates not from adult, which is from Latin a-dolescere, to grow up, mature, a combination of a, "to", dolere, "work", and the processing combound sc), but from the Latin ad-ulterare (to commit adultery, adulterate/falsify, a combination of ad, "at", and ulter, "above", "beyond", "opposite", meaning "on the other side of the bond of marriage"). (Longman Dictionary of Latin, Berlin 1950)
A marriage in which both spouses agree that it is acceptable for either partner to have sexual relationships with other people other than their spouse is a form of nonmonogamy. The resulting sexual relationships the husband or wife has with other people, although could be considered to be adultery in some legal jurisdictions, are not treated as such by the spouses.
Some cultures have a distinguished interpretation of the term infidelity: in some legal systems, it might be tolerated as long as it does not fit the jurisdiction's legal definition of adultery.
There is some debate about whether the desire to commit adultery, like the compulsive desire to consume alcohol, results from a mental disorder. (Is Cheating A Mental Disorder-)
Penalties for adultery
Historically, adulterers have been subject to severe sanctions, including the death penalty, and adultery has been grounds for divorce under fault-based divorce laws. In some places, the method of punishment for adultery is stoning to death.
In the original Napoleonic Code, a man could ask to be divorced from his wife if she committed adultery, but the philandery of the husband was not a sufficient motive for divorce unless he had kept his concubine in the family home.
In some jurisdictions, including Korea, Taiwan and Mexico, adultery is illegal. In the United States, laws vary from state to state. For example, in Pennsylvania, adultery is technically punishable by 2 years of imprisonment or 18 months of treatment for insanity (for history, see Hamowy) (criminal statute repealed 1972), while in Michigan the Court of Appeals, the state's second-highest court, ruled that a little-known provision of state criminal law means that adultery carries a potential life sentence. In Maryland, adultery is punishable by a fine of $10. That being said, such statutes are typically considered blue laws and are rarely, if ever, enforced. In the U.S. Military, adultery is a potential court-martial offense only if the actions of the accused were "to the prejudice of good order and discipline" or "of a nature to bring discredit upon the armed forces". This law has been applied to cases where both partners were members of the military, particularly where one was in command of the other, or one partner and the other's spouse. The enforceability of criminal sanctions for adultery is questionable in light of Supreme Court decisions since 1965 relating to privacy and sexual intimacy, and particularly in light of Lawrence v. Texas, which protected the right of privacy for consenting adults. Because of this, Adultery is generally considered to no longer be illegal in the United States.
In Canadian law, adultery is defined under the Divorce Act. Though the written definition sets it as extramarital relations with someone of the opposite sex, the Civil Marriage Act gave grounds for a British Columbia judge to strike that definition down. In a 2005 case of a woman filing for divorce, her husband had cheated on her with another man, which the judge felt was equal reasoning to dissolve the union.
In Indian law, adultery is defined as sex between a man and a woman without the consent of the woman's husband. The man is prosecutable and can be sentenced for up to 5 years (even if he himself was unmarried) whereas the married woman can not be jailed . Men have accused of gender discrimination in that women can never be prosecuted for adultery . The National Commission of Women has criticized this British era law of being anti-feminist as it treats women as the property of their husbands and has consequentially recommended deletion of the said law or reducing it to a civil offense, but the Government of India is yet to act . Extra marital sex without the consent of one's partner can be a valid grounds for monetary penalty on government employees, as ruled by the Central Administrative Tribunal .
Apart from formal punishment, historically adulterers have suffered from society's disapproving attitudes toward them. The nature of these attitudes vary widely depending on local culture, religion and values, and how seriously the adulterer regards the opinions of others. Often adultery might be overlooked and tacitly accepted by others aware.
Adultery in selected cultural or religious traditions
Historically, adultery was rigorously condemned and punished, usually only as a violation of the husband's rights. Among such peoples the wife was commonly reckoned as the property of her spouse, and adultery was therefore identified with theft. But it was theft of an aggravated kind, as the property which it would spoliate was more highly appraised than other chattels. It is not the seducer alone who suffers. Dire penalties are visited upon the offending wife by her wronged spouse, and in many instances she is made to endure a bodily mutilation which will, in the mind of the aggrieved husband, prevent her from ever being a temptation to other men again (Schoolcraft, Historical and Statistical Information Respecting the History, Condition and Prospects of the Indian Tribes of the United States, I, 236; V, 683, 684, 686; also H.H. Bancroft, The Native Races of the Pacific States of North America, I, 514). If, however, the wronged husband could visit swift and terrible retribution upon the adulterous wife, the latter was allowed no cause against the unfaithful husband; and this discrimination found in the practices of ancient peoples is moreover set forth in nearly all ancient codes of law. The Laws of Manu are striking on this point: in ancient India, "though destitute of virtue or seeking pleasure elsewhere, or devoid of good qualities, yet a husband must be constantly worshipped as a god by a faithful wife"; on the other, hand, "if a wife, proud of the greatness of her relatives or [her own] excellence, violates the duty which she owes to her lord, the king shall cause her to be devoured by dogs in a place frequented by many" (Laws of Manu, V, 154; VIII, 371).
In the Greco-Roman world there were stringent laws against adultery, but this applied to those having sex with a married woman. A married man having sex with a slave or an un-married woman was not a crime. The lending of wives practiced among some peoples was, as Plutarch tells us, encouraged also by Lycurgus, though from a motive other than that which actuated the practice (Plutarch, Lycurgus, XXIX). The recognized license of the Greek husband may be seen in the following passage of the Oration against Neaera, the author of which is uncertain, though it has been attributed to Demosthenes: "We keep mistresses for our pleasures, concubines for constant attendance, and wives to bear us legitimate children and to be our faithful housekeepers. Yet, because of the wrong done to the husband only, the Athenian lawgiver Solon allowed any man to kill an adulterer whom he had taken in the act" (Plutarch, Solon).
In the early Roman Law the jus tori belonged to the husband. There was, therefore, no such thing as the crime of adultery on the part of a husband towards his wife. Moreover, this crime was not committed unless one of the parties was a married woman (Dig., XLVIII, ad leg. Jul.). It is well known that the Roman husband often took advantage of his legal immunity. Thus we are told by the historian Spartianus that Verus, the imperial colleague of Marcus Aurelius, did not hesitate to declare to his reproaching wife: "Uxor enim dignitatis nomen est, non voluptatis." ('Wife' connotes rank, not sexual pleasure) (Verus, V).
Later in Roman history, as the late William E.H. Lecky has shown, the idea that the husband owed a fidelity similar to that demanded of the wife must have gained ground, at least in theory. This Lecky gathers from the legal maxim of Ulpian: "It seems most unfair for a man to require from a wife the chastity he does not himself practice" (Codex Justin., Digest, XLVIII, 5-13; Lecky, History of European Morals, II, 313).
In Judaism, adultery was forbidden in the seventh commandment of the Ten Commandments, but this did not apply to a married man having relations with an unmarried woman. Only a married woman engaging in sexual intercourse with another man was considered to be adultery, in which case both the woman and the man were considered guilty .
In the Mosaic Law, as in the old Roman Law, adultery meant only the carnal intercourse of a wife with a man who was not her lawful husband. The intercourse of a married man with a single woman was not considered adultery. The penal statute on the subject, in Leviticus, 20:10, makes this clear: "If any man commit adultery with the wife of another and defile his neighbor's wife, let them be put to death both the adulterer and the adulteress" (see also Deuteronomy 22:22). This was quite in keeping with the occasional practice of polygamy among the Israelites (which is no longer practiced).
In halakha (Jewish Law) the penalty for adultery is stoning for both the man and the woman, but this is only enacted when there are two independent witnesses who warned the offenders prior to the crime being committed. In the past, the legal standards for capital punishment were so high that a court that executed one person in seven (or, according to another account, seventy) years, was considered a bloodthirsty court. Although this penalty technically still applies, today Jewish courts do not execute anyone for any reason. Halakha forbids a man to continue living with a wife who cheated on him; he is obliged to give her a get or bill of divorce. Neither is the adulteress permitted to the adulterer, who must also give her a bill of divorce if he married her.
The position in Christianity, which arose out of Judaism, comes from the Torah, the first five books of the Christian Old Testament. The Torah explicitly forbids adultery, describing it as an act punishable by death. (Leviticus|20:10) It is also forbidden by the Ten Commandments, which are considered to be the basis of all Jewish Law.
In the accounts of Mark 10:11-12 and Luke 16:18, Jesus taught that a man who divorces his wife and marries another, has committed adultery. In the account of Matthew 5:32 and Matthew 19:9, Jesus makes an exception for cases of marital infidelity on the part of the wife.
In Matthew 5:28, expresses that adultery is committed in the heart by a man who looks with lust at a woman, and made no distinction about whether the woman was married or not.
The modern Catechism of the Catholic Church expresses: "Adultery refers to marital infidelity. When two partners, of whom at least one is married to another party, have sexual relations—even transient ones—they commit adultery." Catechism of the Catholic Church, 2380 It continues on to say that through adultery a person "does injury to the sign of the covenant which the marriage bond is, transgresses the rights of the other spouse, and undermines the institution of marriage by breaking the contract on which it is based." Catechism of the Catholic Church, 2381
According to Islam, adultery is a violation of a marital contract and one of the major sins. In Islam; adultery includes sexual intercourse by a married person, man or woman. Fornication and adultery are both included in the Arabic word 'Zina'. As they belong primarily to the same category of crimes, entail the same social implications and have the same effects on the spiritual personality of a human being, both, in principle, have been given the same status by the Qur'an. The hadith states that the punishment of stoning to death is prescribed for a married person who commits adultery.
"Do not go near to adultery. Surely it is a shameful deed and evil, opening roads (to other evils)" (Quran 17:32).
"Say, 'Verily, my Lord has prohibited the shameful deeds, be it open or secret, sins and trespasses against the truth and reason"' (Quran 7:33).
"Women impure are for men impure, and men impure are for women impure and women of purity are for men of purity, and men of purity are for women of purity." (Quran 24:26)
Although, marrying up to 4 wives and many more as "traveling" marriages which may last even 24 hours is not considered an adultery.
In Pakistan, adultery has been criminalized by a law called the Hudood Ordinance, which specifies a maximum penalty of death, although only imprisonment and corporal punishment have ever actually been used. The Ordinance has been particularly controversial because under it a woman making an accusation of rape must provide extremely strong evidence to avoid being charged under with adultery. The same kinds of laws have been in effect in some other Muslim countries, such as Saudi Arabia. However, in recent years high-profile rape cases in Pakistan have given the Hudood Ordinance more exposure than similar laws in other countries. Hudood laws open to change in Pakistan Conviction is only possible with a minimum of four witnesses.
Proving Adultery under Islam Law can be a very difficult task as Islamic law requires the accuser to produce four eye witnesses to the act of sexual intercourse, each whom should have a good reputation regarding truthfulness and honesty.
- Germany: § 1353 Abs. 1 S. 2 BGB
- MinnesNew York section 255.17.
- North Carolina Statute 14-184.
- Minnesota Statute section 609.36.
- Longman Dictionary of Latin, Berlin 1950
- Is Cheating A Mental Disorder.
- Leviticus 20:10
- Catechism of the Catholic Church, 2380
- Catechism of the Catholic Church, 2381
- Hudood laws open to change in Pakistan, July 2005
- Best Practices: Progressive Family Laws in Muslim Countries (August 2005} 
- Hamowy, Ronald. Medicine and the Crimination of Sin: "Self-Abuse" in 19th Century America. pp2/3 
- Moultrup, David J. (1990). Husbands, Wives & Lovers. New York: Guilford Press.
- Glass, S. P., & Wright, T. L. (1992). Justifications for extramarital relationships: The association between attitudes, behaviors, and gender. Journal of Sex Research, 29, 361-387.
- Jack Goody A Comparative Approach to Incest and Adultery The British Journal of Sociology, Vol. 7, No. 4 (Dec., 1956), pp. 286-305 doi:10.2307/586694
- Pittman, F. (1989). Private Lies. New York: W. W. Norton Co.
- Rubin, A. M., & Adams, J. R. (1986). Outcomes of sexually open marriages. Journal of Sex Research, 22, 311-319.
- Vaughan, P. (1989). The Monogamy Myth. New York: New Market Press.
- Blow, Adrian J, Hartnett, Kelley. (Apr 2005). Infidelity in Committed Relationships I: A Methodological Review. Journal of Marital and Family Therapy. 
- Blow, Adrian J, Hartnett, Kelley. (Apr 2005). Infidelity in Committed Relationships II: A Substantive Review. Journal of Marital and Family Therapy.