The executive is typically a cabinet, and headed by a prime minister who is considered the head of government, but parliamentarism has also been practised with privy councils and the Senate of Finland. The prime minister and the ministers of the cabinet typically have their background in the parliament and may remain members thereof while serving in cabinet. The leader of the leading party, or group of parties, in the parliament is often appointed as the prime minister.
In many countries, the cabinet, or single members thereof, can be removed by the parliament through a vote of no confidence. In addition, the executive often can dissolve the parliament and call extra-ordinary elections.
Under the parliamentary system the roles of head of state and head of government are more or less separated. In most parliamentary systems, the head of state is primarily a ceremonial position, often a monarch or president, retaining duties that aren't politically divisive, such as appointments of civil service.
In many parliamentary systems, the head of state may have reserve powers which are usable in a crisis. In most cases however, such powers are (either by convention or by constitutional rule) only exercised upon the advice and approval of the head of government.
Parliamentary systems vary as to the degree to which they have a formal written constitution and the degree to which that constitution describes the day to day working of the government. They also vary as to the number of parties within the system and the dynamics between the parties. Also, relations between the central government and local governments vary in parliamentary systems, they may be federal or unitary states.
Parliamentarism may also be heeded for governance in local governments. An example is the city of Oslo, which has an executive council as part of a parliamentary system.
The Westminster System is a particular type of parliamentary system that developed out of parliamentary democracy as practised at Westminster in London and was promulgated as the dominant form of government throughout the British Empire, many of whose colonies, since gaining their independence, have become Commonwealth countries. In this model the head of state has considerable reserve powers which have been limited in practice by convention rather than explicit constitutional rule.
