Constitutional monarchy is a kind of monarchy founded under a constitutional system that recognizes the King, Queen, or Emperor as head of state. A modern constitutional monarchy typically uses the concept of trias politica, or political triad. This means the king is merely a symbolic chair of the executive branch. If a king has full governmental power, he is called absolute monarchy or absolute monarchy.

Today, constitutional monarchy is usually combined with representative democracy. Therefore, the kingdom is still under the rule of the people but the king has a traditional role in a country. In essence the prime minister, a leader elected by the people, who governs the country and not the King. Nevertheless, there are also kings who join the undemocratic kingdom. For example, during World War II, the Emperor of Japan joined the kingdom of soldiers led by a dictator.