Delegates to the Constitutional Convention in 1787 argued over a lot of things, but one of their biggest debates was over how the United States should elect its president.

Some among the Founding Fathers believed that direct nationwide election by the people would be the most democratic method. Others argued that a straightforward popular vote was unfair, as it would give too much power to larger, more populous states. They also worried that public opinion could be too easily manipulated, and feared direct election might lead to a tyrannical leader determined to grab absolute power for himself.

The result of this struggle was the Electoral College, the system by which the American people vote not for president and vice president, but for a smaller group of people, known as electors. These electors then cast their votes directly for president and vice president, at a meeting held several weeks after the general election.

There are 538 total electors, including one for each U.S. senator and representative and three electors representing the District of Columbia, and presidential candidates need a majority of 270 votes to win the White House. Most of the time—but not always—the winner of the Electoral College is also the winner of the popular vote.

Article II, Section 1 of the Constitution states that electors can’t be a member of Congress, or hold federal office, but left it up to individual states to figure out everything else. According to the 14th Amendment, ratified after the Civil War, electors also can’t be anyone who has “engaged in insurrection or rebellion against the United States, or given aid or comfort to its enemies.”

The Constitution gave each state a number of electors equal to the combined total of representatives and senators who represent that state in the U.S. Congress. State legislatures are responsible for choosing electors, but how they do this varies from state to state. Until the mid-1800s, it was common for many state legislatures to simply appoint electors, while other states let their citizens decide on electors.

Today, the most common method of choosing electors is by state party convention. Each political party’s state convention nominates a slate of electors, and a vote is held at the convention. In a smaller number of states, electors are chosen by a vote of the state party’s central committee.

Either way, political parties usually choose people whom they want to reward for their service to and support of the party. Electors can be elected officials or party leaders in the state, or people who have some kind of personal or professional connection with the party’s candidate.

After this initial phase of the process, each party’s presidential candidate emerges with their own slate of potential electors. On Election Day, when Americans vote for the presidential and vice presidential candidates of a political party, they are actually voting for the slate of electors who have pledged to cast their votes for that party. Electors’ names may or may not appear on the ballot beneath the names of the candidates, depending on the election rules and the format of the ballots in each state.

Then, on the first Monday after the second Wednesday in December, members of the Electoral College meet in their respective states and cast their official votes for president and vice president. Forty-eight states and the District of Columbia have a winner-take-all system, in which the party whose candidate wins the popular vote in a state appoints all that state’s electors to the Electoral College.

Maine and Nebraska have a “district system.” They appoint electors depending on who won the popular vote in each congressional district, plus two electors who are pledged to vote for the overall winner of the state’s popular vote.

The Constitution doesn’t require electors to vote according to the results of the popular vote in their states, and there is no federal law that requires this. But a number of states have passed laws that threaten to punish so-called “faithless electors,” who do not vote according to the state’s popular vote.

Faithless electors have never decided an election, and more than 99 percent of electors in U.S. history have voted as they pledged to do. But as recently as 2016, seven electors broke with their state on the presidential ballot, and six did so on the vice presidential ballot. Some of these faithless electors were replaced or fined for their rogue votes, but their votes did not affect the election’s outcome.

In 2020, the U.S. Supreme Court ruled that the Constitution does not require that people elected to serve in the Electoral College be free to vote as they choose. Instead, the Court held, states have the constitutional power to force electors to vote according to their state’s popular vote. But while the ruling says states can prevent faithless electors, it does not require that they do so.

At the time of the Court’s decision, 32 states had passed laws that bind electors, while 18 states had laws on the books giving electors the freedom to vote independently—ensuring that in more ways than one, the Electoral College could continue to provide drama for the foreseeable future.