A monarchy is a hereditary form of government in which political power is legally passed on to the family members of the monarch, a head of state who rules for life. While monarchs gain their power depending on specific succession laws, they can also gain their authority via election.
Monarchies were the most common form of government until the 20th century, when republics replaced many monarchies, notably at the end of World War I. As of 2025, forty-three sovereign nations in the world have a monarch, including fifteen Commonwealth realms that share King Charles III as their head of state. Other than that, there is a range of sub-national monarchical entities. Most of the modern monarchies are constitutional monarchies, retaining under a constitution unique legal and ceremonial roles for monarchs exercising limited or no political power, similar to heads of state in a parliamentary republic.