The Royal Prerogative is a body of customary authority, privilege, and immunity, recognised in common law and, sometimes, in civil law jurisdictions possessing a monarchy as belonging to the King or Queen alone. It is the means by which some of the executive powers of government, possessed by and vested in a monarch with regard to the process of governance of their state, are carried out. Individual prerogatives can be abolished by Parliament, although in the UK a special procedure applies.

Though some republican heads of state possess similar powers, they are not coterminous, containing a number of fundamental differences . See reserve powers.

While prerogative powers were originally exercised by the monarch acting alone, and do not require parliamentary consent, they are now always exercised on the advice of the Prime Minister or the Cabinet, who is then accountable for the decision to Parliament. There may be situations in which the monarch could choose to exercise the Royal Prerogative without the advice of the Prime Minister and the Cabinet. Such situations are extremely rare, and could only occur in emergencies. In most liberal-democratic constitutional monarchies, such actions would precipitate a constitutional crisis.

Not all constitutional monarchs have royal prerogative that can be exercised independently however. For example, the King of Sweden and the Emperor of Japan have specific government duties that cannot be exercised with any degree of individual discretion, no matter what the circumstance.