When will we know the results?

Congress is made up of two parts - the lower chamber, the House of Representatives and the upper chamber, the Senate.

To win a majority in the House, a party needs 218 seats. In the Senate, a party needs 51 seats for an outright majority. But if the upper chamber is split 50-50, the vice-president has a tie-breaking vote, which gives their party control of it.

The first results to come in won't tell us much about the overall result because these races are in places considered safe bets for Republicans (Kentucky and Indiana) or Democrats (Vermont).

Throughout the night, BBC analysts will focus on the competitive races which will give an indication of how well things are going for Trump.