A constitutional monarchy is a form of monarchy in which the sovereign exercises authority in accordance with a written or unwritten constitution. Constitutional monarchy differs from absolute monarchy (in which a monarch holds absolute power), in that constitutional monarchs are bound to exercise their powers and authorities within the limits prescribed within an established legal framework. Constitutional monarchies range from countries such as Morocco, where the constitution grants substantial discretionary powers to the sovereign, to countries such as Japan where the monarch retains no formal authorities.
Constitutional monarchy may refer to a system in which the monarch acts as a non-party political head of state under the constitution, whether written or unwritten. While most monarchs may hold formal authority and the government may legally operate in the monarch's name, in the form typical in Europe the monarch no longer personally sets public policy or chooses political leaders. Political scientist Vernon Bogdanor paraphrasing Thomas Macaulay, has defined a constitutional monarch as "A sovereign who reigns but does not rule".
In addition to acting as a visible symbol of national unity, a constitutional monarch may hold formal powers such as dissolving parliament or giving royal assent to legislation. However, the exercise of such powers is largely strictly in accordance with either written constitutional principles or unwritten constitutional conventions, rather than any personal political preference imposed by the sovereign. In The English Constitution, British political theorist Walter Bagehot identified three main political rights which a constitutional monarch may freely exercise: the right to be consulted, the right to encourage, and the right to warn. Many constitutional monarchies still retain significant authorities or political influence however, such as through certain reserve powers, and may also play an important political role.
The oldest constitutional monarchy dating back to ancient times was that of the Hittites. They were an ancient Anatolian people that lived during the Bronze Age whose king or queen had to share their authority with an assembly, called the Panku, which was the equivalent to a modern-day deliberative assembly or a legislature. Members of the Panku came from scattered noble families who worked as representatives of their subjects in an adjutant or subaltern federal-type landscape.