A president is a leader of an organization, company, club, trade union, university, or country.

Etymologically, a president is one who presides, who sits in leadership (from Latin pre- "before" + sedere "to sit"; giving the term praeses). Originally, the term referred to the presiding officer of a ceremony or meeting (i.e., chairman), but today it most commonly refers to an official. Among other things, "President" today is a common title for the heads of state of most republics, whether popularly elected, chosen by the legislature or by a special electoral college.

Presidents in countries with a democratic or representative form of government are usually elected for a specified period of time and in some cases may be re-elected by the same process by which they are appointed, i.e. in many nations, periodic popular elections. The powers vested in such presidents vary considerably. Some presidencies, such as that of Ireland, are largely ceremonial, whereas other systems vest the President with substantive powers such as the appointment and dismissal of Prime Ministers or cabinets, the power to declare war, and powers of veto on legislation. In many nations the President is also the Commander-in-Chief of the nation's armed forces, though once again this can range from a ceremonial role to one with considerable authority.