A monarchy is a form of government in which supreme power is absolutely or nominally lodged with an individual, who is the head of state, often for life or until abdication. The person who heads a monarchy is called a monarch.
Monarchy was the most common form of government into the 19th century, but it is no longer prevalent, at least at the national level. Monarchy now often takes the form of a constitutional monarchy, in which the monarch retains a unique legal and ceremonial role, but exercises limited or no political power pursuant to a constitution or tradition which allocates governing authority elsewhere. Currently, 44 nations in the world have monarchs as heads of state. Of these, 16 are Commonwealth realms such as Canada and Australia that recognize the monarch of the United Kingdom as their head of state.
There is no clear definition of monarchy. Even characteristics most commonly associated with monarchies are not universal. For example, monarchies are often though of as highly centralized forms of absolute power. But holding unlimited political power in the state is not the defining characteristic, as many constitutional monarchies such as the United Kingdom and Thailand are considered monarchies yet their monarchs have limited political power. Hereditary rule is often a common characteristic, but some monarchs are elected (e.g., the Pope), and some states with hereditary rulers are nevertheless considered republics (e.g., the Dutch Republic).
Most states only have a single person acting as monarch at any given time, although two monarchs have ruled simultaneously in some countries, a situation known as diarchy. Historically, this was the case in the ancient Greek city-state of Sparta or 17th-century Russia, and there are examples of joint sovereignty of spouses or relatives (such as William and Mary in the Kingdoms of England and Scotland).
Queen Elizabeth II
Queen Elizabeth II is the monarch of the United Kingdom.