A presidential system, or single executive system, is a form of government in which a head of government (president) leads an executive branch that is separate from the legislative branch in systems that use separation of powers. This head of government is in most cases also the head of state. In presidential countries, the head of government is elected and is not responsible to the legislature, which cannot (usually) in normal circumstances dismiss the president. Such dismissal is possible, however, in uncommon cases, often through impeachment.
The title "president" has persisted from a time when such a person personally presided over the governing body, as with the President of the Continental Congress in the early United States, prior to the executive function being split into a separate branch of government.
A presidential system contrasts with a parliamentary system, where the head of government comes to power by gaining the confidence of an elected legislature. There are also hybrid systems such as the semi-presidential system, used in the former Weimar Republic, France, and Poland.
Countries that feature a presidential or semi-presidential system of government are not the exclusive users of the title of president. Heads of state of parliamentary republics, largely ceremonial in most cases, are called presidents. Dictators or leaders of one-party states, whether popularly elected or not, are also often called presidents.
Presidentialism is the dominant form of government in the mainland Americas, with 19 of its 22 sovereign states being presidential republics, the exceptions being Canada, Belize, and Suriname. It is also prevalent in Central and southern West Africa and in Central Asia. By contrast, there are very few presidential republics in Europe, with Belarus and Cyprus being the only examples. Oceania is the only continent that has no presidential republics.