The Constitution Act of 1867, originally the British North America Act, a statute enacted 29 March 1867 by the British Parliament, provided for Confederation of the Province of Canada (Ontario and Québec), Nova Scotia and New Brunswick into a federal state with a parliamentary system modelled on that of Britain. Rupert's Land was acquired in 1870, and 6 provinces were added to the original 4: Manitoba (1870), British Columbia (1871), Prince Edward Island (1873), Alberta and Saskatchewan (1905), and Newfoundland (1949). The Act does not contain the entire Constitution of Canada. Complementing its text are British and Canadian statutes having constitutional effect (eg, the Canada Elections Act), and certain unwritten principles known as "the conventions of the constitution." Conventions such as the power vested in the Crown to dissolve Parliament and call a general election are usually exercised on the advice of the prime minister.

The Act outlines the distribution of powers between the central Parliament (s91, eg, over banking, interest, criminal law, the postal system and the armed forces) and the provincial legislatures (s92, eg, over property; most contracts and torts; local works, undertakings and businesses). Because of the breadth or generality of the legislative powers conferred, occasionally a direct conflict arises between provincial and federal laws regulating the same things (eg, security frauds). By paramountcy, federal law prevails. In the case of concurrent powers, exercisable by both jurisdictions, federal paramountcy prevails in matters involving agriculture and immigration (s95), but provincial in old-age pensions (s94A). Unallocated powers (eg, aeronautics, radio, official languages) go to the federal government rather than to the local units as in the US and Australia. The federal peace, order and good government power embraces these "residuary" areas and matters falling under "national dimensions" and "emergencies." "National dimensions" signifies that selected matters originally of a local nature and under provincial jurisdiction (eg, day-to-day health care) can, through altered circumstances, such as an epidemic, acquire a new aspect transcending provincial competence and thereby become subject to federal jurisdiction. In wartime virtually all provincial powers may come under central control.

In 1976 the Supreme Court of Canada decided that Parliament also possessed what amounted to a peacetime emergency power to impose national wage and price controls to combat serious national inflation. Unlike the American constitution, the Constitution Act contains no postulate that all local units are constitutionally equal. The Prairie provinces, for example, unlike the original 4, did not possess their lands and minerals for 25 years after their acquisition of provincial status.

Judicial interpretation has had a substantial effect on the ambit of provincial and federal powers. Until appeals to Britain were abolished in 1949, influential judges on the Judicial Committee of the Privy Council often expansively interpreted provincial powers, such as those over property and civil rights, when they came into conflict with federal powers over peace, order and good government or the regulation of trade and commerce. They sought thereby to offset the excessive centralism they perceived in the BNA Act (eg, the federal veto over any provincial statute in s90) and to preserve a viable federal system. Since 1949 the Supreme Court has pursued a more centralist interpretation. In 1980, the omission of a domestic amending formula in the BNA Act led to a constitutional crisis when Prime Minister Pierre Trudeau attempted unilaterally to patriate the Constitution, by the "joint address" procedure, without provincial consent. When the Supreme Court decided in September 1981 that his proposal was unconstitutional in the conventional sense, Trudeau relented, with "patriation" finally being achieved in April 1982 by federal-provincial consensus.

See also Constitutional History; Constitutional Law; Constitution Reference. See document Constitution Act, 1982