Parliamentary and Presidential systems
Systems of gov't can be classified as either parliamentary or presidential. The terms refer to the type of relationship between the executive and the legislature.
In parliamentary systems, the executive and the legislature are interconnected. There is no strict separation of powers. The gov't (executive) is normally chosen from the representatives of the majority party (or coalition group, if no single party has a majority) elected to legislature (the Parliament or assembly). The government is accountable for its actions to the legislature and it is dependent upon the continued support of the legislature to remain in office.
In presidential systems the legislature and executive are distinct (a clear separation of powers). The head of the executive, the President, is chosen by the electorate rather than by the legislature. Presidents do not sit in, and cannot normally be removed by, the legislature. The President acts as head of government and as ceremonial head of state.
Most European countries have parliamentary systems whereas the USA has the best known example of a presidential system. Presidential systems can also be found in Latin American states and in some Asian and African countries. Describing a system of gov't as 'presidential', however, does not necessarily that the country has a president rather than a monarch as its head of state. Ireland and Germany, for example, both have presidents as heads of state but they both operate parliamentary systems of gov't.
Differences between parliamentary and presidential systems
The UK
The USA
The executive and the legislature are tightly linked. The executive - the gov't ministers - sit in one of the two Houses of Parliament (the Commons or the Lords). Ministers take part in debate and vote together with the other members of Parliament.
The executive is not independent of Parliament - the HoCs can overthrow the gov't by a vote of no