The royal prerogative is the residue of power once exercised by the Crown. In modern Canadian law, some historic prerogative powers have been codified as part of Canada’s written constitutional law. Others persist in a form governed by constitutional conventions. Most others have been displaced by legislation, through the exercise of parliamentary supremacy. Exactly what is required before this displacement by statute arises is, however, an area of considerable uncertainty in Canadian law. What is clear is that the royal prerogative remains a source of executive authority in several special subject areas, especially defence and foreign relations. Some exercises of the remaining prerogatives constitute matters of high policy, whereas others may affect the interests and rights of individuals. Where exercises of the prerogative do affect interests and rights, the prerogative has been treated no differently than any other exercise of executive power. Specifically, it has been subject to judicial review.