Parliamentary system

World's states coloured by systems of government:
Republic:
  Presidential republic: President heads the government and is independent of the legislature
  Parliamentary republic: President is mostly or entirely ceremonial; ministry is accountable to the legislature
  Semi-presidential republic: President has some executive powers and is independent of legislature; remaining executive power is vested in ministry accountable to the legislature
  Republic with an executive head of state either accountable to the legislature or elected by it but not accountable to it
  One-party state: Power is constitutionally linked to a single political party

Monarchy:
  Constitutional monarchy: Monarch is mostly or entirely ceremonial; ministry is accountable to the legislature
  Semi-constitutional monarchy: Monarch holds significant executive or legislative power; remaining executive power is vested in the ministry
  Absolute monarchy: Monarch heads the government

  Military junta: Committee of military leaders controls the government; constitutional provisions are suspended
  Provisional government: No constitutionally defined basis to current regime
  Dependent territories and places without governments

Note: this chart represent de jure systems of government, not the de facto degree of democracy.

A parliamentary system, or parliamentary democracy, is a system of democratic government where the head of government (who may also be the head of state) derives their democratic legitimacy from their ability to command the support ("confidence") of the legislature, typically a parliament, to which they are accountable.

In a parliamentary system, the head of state and head of government are usually two separate positions, with the head of state serving as a ceremonial figurehead with little if any power, while all of the real political power is vested in the head of government. This is in contrast to a presidential system, which features a president who is usually both the head of state and the head of government and, most importantly, does not derive their legitimacy from the legislature.

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 across the Caribbean, being the form of government of 10 of its 13 island states, and in Oceania. Elsewhere in the world, parliamentary governments 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.