The criminal offense of unlawful assembly generally means the assembly of multiple persons resulting in conduct that (1) is intended to commit a breach of the peace or other unlawful act; (2) creates an immediate danger of damage to property or injury to persons; (3) substantially obstructs law enforcement or other governmental functions or services; (4) is tumultuous or violent and likely to cause public alarm; or (5) deprives any person of a legal right or disturbs any person in the enjoyment of a legal right by using force or the threat of force.

Unlawful assembly laws vary from state to state and some states have related offenses such as rioting, riots and routs, participating in a riot, inciting a riot, failing to disperse, and disturbing the peace. The criminal offense of unlawful assembly may be included in the definition of one or more of these offenses or may be a separate criminal offense. These laws are generally located in a state’s statutes—often in the penal or criminal code.

In Maine, the criminal offense of unlawful assembly is addressed under Maine's penal code, specifically in the statutes concerning 'Riots and Disorderly Conduct.' According to Maine law, a person is guilty of unlawful assembly if they intentionally or recklessly assemble with five or more other persons for the purpose of engaging in conduct constituting a riot, or if they fail to disperse after being ordered to do so by a law enforcement officer when five or more persons are participating in a riot. A riot is defined as a group of five or more people engaging in tumultuous or violent conduct that creates a grave risk of causing public alarm. The offense of unlawful assembly is considered a Class D crime, which can result in fines and potential jail time. Maine law also covers related offenses such as failure to disperse and disorderly conduct, which can be charged under various circumstances that disrupt public peace or order.