The Riot Act is an old piece of English legislation allowing certain officials to declare any assembly of more than twelve persons to be unlawful and order the assembly to disperse within one hour on pain of death. Most sources say it was enacted in 1715, but it was actually enacted in 1714 and went into effect in 1715. This was a period of insurgency in England.

To invoke the Act, the following words had to be read by a "justice or justices of the peace, or by the sheriff of the county, or his under-sheriff, or by the mayor, bailiff or bailiffs, or other head-officer, or justice of the peace of any city or town corporate":

Our Sovereign Lord the King chargeth and commandeth all persons being assembled immediately to disperse themselves, and peaceably to depart to their habitations or to their lawful business, upon the pains contained in the act made in the first year of King George for preventing tumultuous and riotous assemblies. God save the King.

Because the Riot Act was passed during the Colonial period it was inherited by many British colonies. The Act was repealed in Britain in 1973 but a modified version lives on in Canada under sections 64-69 and 33 of the Criminal Code. This Riot Act is similar, but requires rioters to dismiss within 30 minutes and substitutes life imprisonment for the death penalty. A "riot" is defined in the Criminal Code as "an unlawful assembly that has begun to disturb the peace tumultuously".

The expression "to read the riot act" comes from the real Riot Act and means to severely reprimand, as in "I was late for work again, the boss really read me the riot act!".