Start with the Constitution. The basic process of selecting the President of the United States is spelled out in the U.S. Constitution, and it has been modified by the 12th, 22nd, and 23rd amendments. Many additional steps have been added over the years, by custom and by state law -- the process has changed quite a bit over time.

Who Can Run? The President and Vice-President are elected every four years. They must be at least 35 years of age, they must be native-born citizens of the United States, and they must have been residents of the U.S. for at least 14 years. (Also, a person cannot be elected to a third term as President.)

How Do the Political Parties Choose Their Candidates? That's up to the political parties. Most political parties hold conventions, which are large meetings attended by "delegates." Some delegates are selected by state "primary" elections, some are selected by state caucuses (very much like primaries, except with public voting instead of secret ballots), and some are chosen for their prominence in the party. A majority of delegate votes is needed to win the party's nomination. In most cases, the delegates let their chosen presidential candidate select a vice-presidential candidate.

Candidates for President and Vice-President Run Together. In the general election, each candidate for President runs together with a candidate for Vice-President on a "ticket." Voters select one ticket to vote for; they can't choose a presidential candidate from one ticket and a vice-presidential candidate from another ticket.

The Electoral College. The national presidential election actually consists of a separate election in each of the 50 states and the District of Columbia; in these 51 elections, the voters are really voting for "electors" pledged to one of the tickets. These electors make up the "Electoral College." (In most cases, the names of the electors aren't written on the ballot; instead the ballot lets voters choose among "Electors for" each of the tickets, naming the presidential and vice-presidential candidates each slate of electors is pledged to.)

Each state has the same number of electors as it has senators and representatives (there are two senators from each state, but the number of representatives depends on the state population in the most recent census). The District of Columbia, although it isn't a state, also participates in presidential elections -- it currently has three electors.

The People in Each State Vote for Electors in the Electoral College. In most of the states, and also in the District of Columbia, the election is winner-take-all; whichever ticket receives the most votes in that state (or in D.C.) gets all the electors. (The only exceptions are Maine and Nebraska. In these states, just two of the electors are chosen in a winner-take-all fashion from the entire state. The remaining electors are determined by the winner in each congressional district, with each district voting for one elector.)

The Electoral College Votes for the President. The Electoral College then votes for President and for Vice-President, with each elector casting one vote; these votes are called electoral votes. Each elector is pledged to vote for particular candidates for President and Vice-President. In most elections, all the electors vote in accordance with the pledge they made; it is not clear what would happen in the unlikely event that a large number of electors violated their pledge and voted differently.

Normally, one of the candidates for President receives a majority (more than half) of the electoral votes; that person is elected President. That candidate's vice-presidential running mate will then also receive a majority of electoral votes (for Vice-President), and that person is elected Vice-President.

If There's No Electoral College Winner, the House of Representatives Chooses the President. In the rare event that no presidential candidate receives a majority of the electoral votes, then the President is chosen instead by the House of Representatives, from the top three presidential vote-getters in the Electoral College; each state delegation in Congress casts one vote. (The Vice-President would be chosen from the top two vice-presidential vote-getters by the Senate.)

This is bizarre! Does it really work this way? Yes. There are many arguments pro and con the Electoral College, but this system does guarantee that the person elected President has substantial support distributed throughout the U.S. The Electoral College has also been a major factor in the United States' long-term political stability.