An unlawful act. Notable examples include stealing, killing, and rape. Committing crimes typically makes one subject to punishment under the law, often in the form of fines, imprisonment, forced labor, or, in extreme cases, execution. These punishments are usually enacted by a judicial system, but can also be enacted by law enforcement such as police officers.

Someone who commits crimes is a criminal. Some criminals form organizations to carry out more ambitious crimes or evade punishment (such as the mafia), which is a popular topic in fiction.