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 Virginia, the criminal offense of unlawful assembly is addressed under Virginia Code § 18.2-406. This statute defines unlawful assembly as any assembly of three or more persons with the intent to commit a breach of the peace, or wherein any such person unlawfully engages in conduct that has a likelihood to cause a breach of the peace. The law also covers situations where the group's conduct creates an immediate danger of damage to property or injury to persons, substantially obstructs law enforcement or other governmental functions, or is tumultuous or violent, potentially causing public alarm. Additionally, if the assembly results in the deprivation of someone's legal rights or disturbs their enjoyment of these rights through force or threat of force, it may also be considered unlawful. Penalties for participating in an unlawful assembly can range from a Class 1 misdemeanor to a Class 5 felony, depending on the specific actions and outcomes of the assembly. Related offenses, such as rioting or failing to disperse, are also criminalized under separate statutes within the state's penal code.