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 Colorado, the criminal offense of unlawful assembly is addressed under the state's statutes concerning public peace and order. Specifically, Colorado law defines 'inciting riot' and 'engaging in a riot' as separate offenses, which can encompass situations that might be considered unlawful assembly. According to Colorado Revised Statutes (C.R.S.) 18-9-102, a person commits inciting riot if they incite or urge a group of five or more persons to engage in a current or impending riot. Under C.R.S. 18-9-104, a person commits engaging in a riot if they participate in or encourage a riot, which is defined as a public disturbance involving an assemblage of three or more persons which by tumultuous and violent conduct creates grave danger of damage or injury to property or persons or substantially obstructs law enforcement or other government functions. Additionally, the statute C.R.S. 18-9-107 addresses 'disobedience of public safety orders under riot conditions,' requiring individuals to comply with dispersal orders during a riot or unlawful assembly. Penalties for these offenses vary based on the specific conduct and the degree of harm or risk involved.