A Constitution is the system of laws and conventions by which a state governs itself; the basic law of a country; the law of laws. In most countries, the Constitution is written. Great Britain, however, has a constitution that in great part is not written. Canada's Constitution, though similar to the largely unwritten Constitution of Great Britain, is primarily written, notably in sections on the DISTRIBUTION OF POWERS.

The ROYAL PROCLAMATION OF 1763, the QUEBEC ACT (1774), the CONSTITUTIONAL ACT (1791) and the ACT OF UNION (1840) which preceded the BRITISH NORTH AMERICA ACT (1867) are all constitutional Acts concerning Canada. The STATUTE OF WESTMINSTER (1931) recognized the independence of Canada; the Canada Act of 1982 and the Constitution Act of 1982 patriated the Constitution and gave Canada a Charter of Rights and Freedoms and a general amending formula.

Since 17 April 1982, the BNA Act has been styled the Constitution Act of 1867, while the Constitution Acts of 1867 to 1975 and the Constitution Act of 1982 have been collectively titled the Constitution Acts 1867 to 1982. The Constitution of Canada also comprises other legislative documents and decrees, including the British Magna Carta (1215), Bill of Rights (1689), Petition of Right (1629) and Act of Settlement (1701). In its judgement of 28 September 1981, the Supreme Court of Canada noted that the Constitution consists of legislative rules, rules of the common law and constitutional conventions. The first 2 rules make up CONSTITUTIONAL LAW; the conventions, while part of the Constitution and recognized and commented upon by the courts, are not imposed by the courts and are not a source of constitutional law and when they are flouted the remedy is political, not legal.

The Supreme Court in that reference declared that nothing in constitutional law precluded Parliament from presenting an Address to the British Parliament requesting amendment to the Constitution of Canada, but that a constitutional convention nonetheless required that Parliament enjoy substantial support from the provinces before doing so. The Supreme Court provided several examples of such conventions. One of the most important is that of RESPONSIBLE GOVERNMENT, eg, the Cabinet may only stay in power as long as it enjoys the confidence of the House of Commons. According to the Supreme Court, "a convention occupies a position somewhere in between usage or custom on the one hand and a constitutional law on the other," and its main purpose "is to ensure that the legal framework of the Constitution will be operated in accordance with the prevailing constitutional values or principles of the period."