The United States Electoral College is a term used to describe the 538 Presidential electors who meet every four years to cast the official votes for President and Vice President of the United States. The Constitution gives each state legislature the plenary power to choose the electors who shall represent its state in the Electoral College. Through this constitutional authority, each state legislature also has the power to determine how exactly the electors are to be chosen (including the legislature choosing the electors). Presently, every state legislature chooses to allow its electors to be popularly chosen (by a state-wide ballot for slates of electors, who have informally pledged themselves to support a particular Presidential candidate and a particular Vice Presidential candidate) on the day set forth by federal law for that purpose—i.e. Election Day. Presidential electors meet in their respective state capitol buildings—or in the case of Washington, D.C., in the District of Columbia—on the first Monday after the second Wednesday in December (per ). The Electors never meet as a national body. At the 51 separate meetings, held on the same day, the electors cast the electoral votes. As such, the collective concept of the 51 groups is the technical definition of the college. The electoral college system, like the national convention, is an indirect element in the process of electing the president. The Constitution does not require the electors to vote as pledged, but many states have enacted laws that do require their electors to vote as pledged.

The original mechanics of presidential elections were established by Article II, Section 1, Clause 3 of the United States Constitution. The Twelfth Amendment revised those mechanics, requiring that each elector vote separately for President and Vice President. Today, the mechanics of the Presidential election are administered by the National Archives and Records Administration via its Office of the Federal Register.

Electors are chosen by way of elections in each state, and Washington, D.C., held on Election Day. The number of electoral votes of each state is the sum of its number of U.S. Senators (always two) and its U.S. Representatives to which that state is entitled. Washington, D.C. has the same number of votes it would if it had Senators and Representatives, but no more than the least populous state (i.e., three electoral votes). In each state, voters vote for a slate of pre-selected candidates for Presidential Elector, representing the various candidates for President. State ballots, however (for ease of understanding the ballot), are designed to suggest that the voters are casting a ballot for the actual candidates for President. Usually states use what is termed the short ballot, in which a vote for one party (such as Democratic or Republican) is interpreted as a vote for the entire slate of Presidential Electors.

Except for Maine and Nebraska, the entire electoral college vote of a state is won by the slate of electors who receive either a simple majority (50% plus 1 vote between two candidates), or a plurality (the highest individual percentage of the vote where there are three or more candidates) of the whole number of votes cast by the people of the state. In Maine and Nebraska Presidential Electors are chosen by using what is termed the District Method (explained later in this article).

The Presidential Electors of each state, and Washington, D.C., meet to cast their electoral votes 41 days following Election Day. The electors ballot first for President, then for Vice President. On rare occasions, an elector does not cast the electoral vote for the party's national ticket, usually as a political statement; these people are called faithless electors. Each elector signs a document entitled the Certificate of Vote which sets forth the electoral vote of the state (or district). One original Certificate of Vote is sent by certified mail to the Office of the Vice President.

Approximately one month following the casting of the electoral votes, the newly seated U.S. Congress meets in joint session to declare the winner of the election. If a candidate for President receives the vote of 270 or more Presidential Electors, the presiding officer (usually the sitting Vice President) declares that candidate to be the President-elect. Similarly, a candidate for Vice President receiving 270 or more electoral votes is declared to be the Vice President-elect.

The nature of the process and its complication have been critiqued, with its detractors proposing several alternative methods of electing the president. This issue was revisited following the Presidential Election of 2000 when Democratic candidate Al Gore received the plurality of the national vote, but failed to win the majority of the Electoral College. Advocates of the current system have similarly set forth arguments for its advantages.