Electoral college

The collective term for the 538 electors who officially elect the president and vice-president of the United States.

Electors cast their ballot on the first Monday after the second Wednesday in December but never meet as one collective body. Instead they cast their votes in their respective state capitals.

Presidential candidates require a majority of 270 college votes to win the presidency.

The college system was originally conceived before the existence of political parties and was designed to allow the electors to exercise their own judgement on the candidates as independent voters.

Electors are now considered to be representatives of a party and are expected to follow the wishes of the majority of voters in each state.

However, there have been a number of cases in recent elections where at least one elector has voted for a candidate other than the one they were pledged to.

Recently two states, Nebraska and Maine, have also eliminated the "winner takes all" process and instead now divide their electors in accordance with the proportion of the popular vote given to each candidate.

The number of electors each state is allocated is equal to the combined total of its senators and representatives in Congress.

Under the 23rd Amendment, ratified in 1961, the District of Columbia (Washington DC) is allocated the same number of electors as the least populous states.

Before the amendment residents of the US capital were prevented from voting in national elections by Article II of the constitution which says that only "states" are allowed to appoint electors.