What are the differences between parliamentary and presidential forms of government?

In a parliamentary form of government, the executive is usually known as a prime minister. He or she is chosen from the majority party in the parliament, and chooses a cabinet, or ministry, that is sometimes also drawn from parliament. In a presidential form of government, the executive is separate from the legislative. The president usually has some legislative powers, including the veto, but operates independently from the legislature, which may (and indeed often does in the United States) have a majority of members that are drawn from a different party than the president. The United States is the world's oldest presidential government, and it is based upon a system of checks and balances that often places the President at odds with a Congress frequently dominated by the opposition.

One feature of the presidential system in the United States is that it is essentially a two-party system. This feature is not shared by many parliamentary democracies (and indeed some other presidential systems) around the world. Thus many parliamentary systems emphasize coalition-building as a means of governing, and in many cases prime ministers are chosen with the support of coalitions rather than of a single party with an outright majority.

One more significant difference is that prime ministers can often be removed with greater ease than presidents. If the ruling party is driven from power in parliamentary elections, then the prime minister will lose their job as well. In most parliamentary systems, prime ministers can be removed by a vote of "no confidence" by the legislature, which is generally much easier to carry out from a procedural standpoint than the impeachment and removal process by which a president can be removed.