Countries with parliamentary systems may be constitutional monarchies, where a monarch is the head of state while the head of government is almost always a member of parliament, or parliamentary republics, where a mostly ceremonial president is the head of state while the head of government is regularly from the legislature. In a few parliamentary republics, among some others, the head of government is also head of state, but is elected by and is answerable to parliament. In bicameral parliaments, the head of government is generally, though not always, a member of the lower house.
Parliamentarianism is the dominant form of government in Europe, with 32 of its 50 sovereign states being parliamentarian. It is also common in the Caribbean, being the form of government of 10 of its 13 island states, and in Oceania. Elsewhere in the world, parliamentary countries are less common, but they are distributed through all continents, most often in former colonies of the British Empire that subscribe to a particular brand of parliamentarianism known as the Westminster system.
- See also: Parliamentary government formation