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 Pennsylvania, the criminal offense of unlawful assembly is addressed under the state's statutes, specifically within the crimes code. According to 18 Pa.C.S. § 5502, a person commits the offense of unlawful assembly if they assemble with two or more persons for the purpose of engaging in conduct constituting a riot, or they assemble with two or more persons and engage in conduct intended to commit a breach of the peace or an unlawful act. The statute also covers situations where such an assembly causes a person to reasonably fear that such a breach of the peace or unlawful act will occur. The related offenses, such as riot, failure to disperse, and disorderly conduct, are also defined in the Pennsylvania crimes code. For instance, 'riot' is defined under 18 Pa.C.S. § 5501, and it involves an assembly of three or more persons engaging in tumultuous and violent conduct that creates a grave danger of causing public alarm. 'Failure to disperse' under 18 Pa.C.S. § 5503 occurs when a person, being present at the scene of an unlawful assembly or a riot, refuses to obey an official order to disperse. These offenses can carry various penalties, including fines and imprisonment, depending on the severity of the conduct and the specific provisions violated. An attorney can provide more detailed information on how these laws might apply to a particular situation.