The War Measures Act (French: Loi sur les mesures de guerre; 5 George V, Chap. 2) was a statute of the Parliament of Canada that provided for the declaration of war, invasion, or insurrection, and the types of emergency measures that could thereby be taken. The Act was brought into force three times in Canadian history: during the First World War, Second World War and the 1970 October Crisis.

The Act was questioned for its suspension of civil liberties and personal freedoms, including only for Ukrainians and other Europeans during Canada's first national internment operations of 19141920, the Second World War's Japanese Canadian internment, and in the October Crisis. In 1988, it was repealed and replaced by the Emergencies Act.

The October Crisis (French: Crise d'Octobre) refers to a chain of events that started in October 1970 when members of the Front de libération du Québec (FLQ) kidnapped the provincial Deputy Premier Pierre Laporte and British diplomat James Cross from his Montreal residence. These events saw the Prime Minister Pierre Trudeau invoking the War Measures Act for the first time in Canadian history during peacetime.

The Premier of Quebec, Robert Bourassa, and the Mayor of Montreal, Jean Drapeau, supported Trudeau's invocation of the War Measures Act, which limited civil liberties and granted the police far-reaching powers, allowing them to arrest and detain 497 people. The Government of Quebec also requested military aid to support the civil authorities, with Canadian Forces being deployed throughout Quebec.

Although negotiations led to Cross's release, Laporte was murdered by the kidnappers. The crisis affected the province of Quebec, Canada, especially the metropolitan area of Montreal, and ended on December 28.

At the time opinion polls in Quebec and throughout Canada showed widespread support for the usage of the War Measures Act. The response was criticized by prominent politicians such as René Lévesque and Tommy Douglas.

After the crisis, movements that pushed for electoral votes as a means to attain autonomy and independence grew stronger. At the time, support also grew for the sovereignist political party known as Parti Québécois, which formed the provincial government in 1976.