Most states define adultery as “sexual intercourse between a married person and someone other than their spouse”, however this definition can vary from state to state. In North Carolina for example, adultery is defined as any sexual relations between a man and a woman who are not married and cohabitating together, whether legally married to someone else or not. Adultery is one of the most common reasons couples seek divorce.
Most states treat adultery as a “crime against marriage,” subject to religious ramifications as well as being grounds for divorce. In states that do recognize adultery as grounds for divorce, the extra-marital affair must be proved in court. States in which adultery is not considered grounds for divorce are known as no-fault divorce states. It should be noted, however, that even in no-fault states, courts may consider adultery when deliberating property distribution and child custody issues. Some courts even make a distinction between a one-time adulterous act and an on-going affair.
There are still approximately 20 states in the U.S. that have an adultery law on the books, with punishments ranging from a $10 fine to three years in prison. While these laws are rarely enforced, there are cases where adultery laws come into play. A Michigan Appeals Court, for example, ruled that adultery committed under circumstances involving any other felony is punishable by a sentence of up to life imprisonment.
While adultery is considered a form of infidelity, the reverse is not necessarily true: infidelity does not require sexual relations to exist – in fact, infidelity can also include non-sexual behaviors such as flirting and emotional affairs. Allegations of other types of infidelity are typically alleged as emotional abandonment, cruelty, etc.
In other parts of the world adultery laws are strictly enforced and can carry harsh penalties. For example, adultery is treated as a major sin under Islamic law and in some countries violators can be stoned to death.