The President's term of office begins at noon on January 20 of the year following the election. This date, known as Inauguration Day, marks the beginning of the president's and vice president's four-year terms. Before assuming office, the president-elect is constitutionally required to take the presidential oath:

Although it is not required, Presidents traditionally used a Bible to take oath of office (some exceptions: Chester A. Arthur in 1881 and Theodore Roosevelt in 1901 did not use a Bible, while Lyndon B. Johnson in 1963 used a Roman Catholic missal, because there were no Bibles aboard Air Force One).

Although no law requires that the oath of office must be administered by someone, new presidents are traditionally sworn-in by the Chief Justice of the United States. George Washington was sworn-in by Chancellor of New York Robert Livingston while John Tyler, Millard Fillmore, Chester A. Arthur, Theodore Roosevelt, Calvin Coolidge and Lyndon B. Johnson by lesser-capacity judges.

George Washington, the first president, set an unofficial term limit of two terms, which was generally followed by subsequent presidents as precedent. After the twelve-year presidency of Franklin D. Roosevelt, who was elected four times, but died shortly after beginning his fourth term, the Twenty-second Amendment to the Constitution was ratified, barring presidents from being elected more than twice, or once if they served more than half of another president's term. Prior to Roosevelt, several presidents had campaigned for a third term, but none were elected. Harry S. Truman, who was president at the time of the amendment's ratification and thus not subject to its terms, also briefly sought a third term before withdrawing from the 1952 race, although it would have been only his second full term as president.

Since the amendment's ratification, three presidents have served two full terms: Dwight D. Eisenhower, Ronald Reagan, and Bill Clinton. Richard Nixon was elected to a second term, but resigned before completing it; George W. Bush will become the fourth upon completion of his current term on January 20, 2009. Lyndon B. Johnson was the only president under the amendment to be eligible to serve more than two terms in total, having only served for 14 months following John F. Kennedy's assassination. However, he chose not to run in the 1968 election.

Voters in each of the states elect a president on Election Day, set by law as the first Tuesday after the first Monday in November, once every four years; elections for other offices at all levels of government also occur on this date. Each state holds a number of electoral votes that correspond to electors in the Electoral College. Tickets of presidential and vice presidential candidates are shown on the ballot; each vote for the tickets actually corresponds to a vote for a slate of electors chosen by the candidates' political party. In most states, the ticket that wins the most votes in a state wins all of that state's electoral votes, and thus has their slate of electors chosen to vote in the Electoral College. Maine and Nebraska do not use this method, opting instead to give two electoral votes to the statewide winner and one electoral vote to the winner of each Congressional district. Neither state has split electoral votes between candidates as a result of this system in modern elections. In any case, the winning set of electors meets at their state's capital on the first Monday after the second Wednesday in December, a few weeks after the election, to vote, and sends a vote count to Congress.

The vote count is opened by the sitting vice president, acting in his capacity as President of the Senate, and read aloud to a joint session of the incoming Congress, which was elected at the same time as the president. Members of Congress can object to any state's vote count, provided that the objection is supported by at least one member of each house of Congress. A successful objection will be followed by debate; however, objections to the electoral vote count are rarely raised.

In the event that no candidate receives a majority of the electoral vote, the House of Representatives chooses the president from among the top three contenders. However, the House does not vote normally; instead, each state delegation is given only one vote, marginalizing the importance of more populous states. The vice president is chosen through normal voting in the Senate, where each state delegation is already of equal size.

Article Two of the Constitution sets the principal qualifications to be eligible for election as President. A Presidential candidate must:

• be a natural-born citizen of the United States
• be at least thirty-five years old
• have been resident in the United States for at least fourteen years