illegal

Illegal is an adjective used to describe conduct or conditions that are forbidden by law. An act is illegal when it violates statutes, regulations, or recognized legal principles, and is subject to sanctions by the state. Because legal systems differ, what is illegal in one jurisdiction may be lawful elsewhere; examples include theft, assault, and fraud, as well as violations of regulatory schemes such as unauthorized possession of controlled substances, tax evasion, or license breaches.

Illegality covers both criminal offenses and civil or regulatory violations. Some acts are criminal offenses with penalties like fines, imprisonment, or probation; others violate administrative rules and yield civil penalties such as fines or injunctions. In some cases an act can be illegal only in certain contexts, such as trespass or possession of a regulated item without proper authorization.

Enforcement and interpretation vary by jurisdiction. Courts determine whether an act is illegal and prosecutors decide charges. The presence of defenses—such as lack of intent, necessity, or consent—can affect whether an act is treated as illegal in a given case. Laws can also change over time, so acts that were once illegal may become legal, and vice versa, through reforms, legal challenges, or shifts in policy.