A constitutional monarchy is a form of government established under a constitutional system which acknowledges a hereditary or elected monarch as head of state. Modern constitutional monarchies usually implement the concept of trias politica, and have the monarch as the (symbolic) head of the executive branch. Where a monarch holds absolute power, it is known as an absolute monarchy.

Today, constitutional monarchy is almost always combined with representative democracy, and represents theories of sovereignty which place sovereignty in the hands of the people, and those that see a role for tradition in the theory of government. Though the king or queen may be regarded as the government's symbolic head, it is the Prime Minister, whose power derives directly or indirectly from elections, who actually governs the country.

Although current constitutional monarchies are mostly representative democracies, this has not always historically been the case. There have been monarchies which have coexisted with constitutions which were fascist (or quasi-fascist), as was the case in Italy, Japan and Spain, or those in which the government is run as a military dictatorship, as was the case in Thailand.

Some constitutional monarchies are hereditary; others, such as that of Malaysia are elective monarchies.

Present constitutional monarchies

Some constitutional monarchies are:

• Antigua and Barbuda (Queen Elizabeth II)
• Australia (Queen Elizabeth II)
• The Bahamas (Queen Elizabeth II)
• Barbados (Queen Elizabeth II)
• Belgium (King Albert II)
• Belize (Queen Elizabeth II)
• Bhutan (King Jigme Singye Wangchuk)
• Cambodia (King Norodom Sihamoni)
• Canada (Queen Elizabeth II)
• Denmark (Queen Margrethe II)
• Grenada (Queen Elizabeth II)
• Jamaica (Queen Elizabeth II)
• Japan (Emperor Akihito)
• Liechtenstein (Prince Hans-Adam II)
• Luxembourg (Grand Duke Henri)
• Malaysia (Yang di-Pertuan Agong Tuanku Syed Sirajuddin)
• Monaco (Prince Albert)
• The Netherlands (Queen Beatrix)
• New Zealand (Queen Elizabeth II)
• Norway (King Harald V)
• Nepal (King Gyanendra Shaha)
• Papua New Guinea (Queen Elizabeth II)
• Saint Kitts and Nevis (Queen Elizabeth II)
• Saint Lucia (Queen Elizabeth II)
• Saint Vincent and the Grenadines (Queen Elizabeth II)
• The Solomon Islands (Queen Elizabeth II)
• Spain (King Juan Carlos)
• Sweden (King Carl XVI Gustaf)
• Thailand (King Bhumibol Adulyadej)
• Tuvalu (Queen Elizabeth II)
• The United Kingdom (Queen Elizabeth II)

Previous monarchies

France functioned briefly as a constitutional monarchy during the French Revolution. It also was a constitutional monarchy under the reign of Louis XVIII and Charles X, but the latter's attempt at reinstating absolute monarchy led to his fall. Louis-Philippe of France was also a constitutional monarch.

Napoléon Bonaparte, as Emperor of the French, was a constitutional monarch, though he had wide powers and also occasionally abused powers that he did not have.

Prior to the Iranian Revolution in 1979, Iran was a constitutional monarchy Under HIM Mohammad Reza Shah Pahlavi.