Why the US midterms matter even if you don't live in America
More than 230 million eligible voters across the United States can head to the polls on Tuesday to decide who will represent them in Congress.
All 435 House of Representatives seats and 35 of the Senate’s 100 seats are being contested . Voters in 36 states will also elect governors. Republicans currently hold both chambers.
Here is what is expected on the day:
Voting hours are determined and set by each state.
The first polls are set to open in Vermont at 5am (10:00 GMT). Voting in New Jersey, Virginia, Connecticut and Kentucky will start at 6am (11:00 GMT).
Voting in Georgia, Florida, Pennsylvania and New York will start between 6am (11:00 GMT) and 7am (12:00 GMT), while Ohio and North Carolina will see voting start at 6:30am (11:30 GMT).
In Michigan, polls will open at 7am (12:00 GMT).
Polls close in waves across the country, with the earliest closures at 6pm (23:00 GMT) in Indiana and Kentucky.
Voting in Michigan closes at 8pm and in Kansas at 7pm local time (both 01:00 GMT on Wednesday), while polls in Iowa close at 8pm (02:00 GMT on Wednesday).
Alaska is the last to close, at around 1am Eastern Time (06:00 GMT) on Wednesday.
The first results could start arriving on Tuesday as polls begin to close.
Results will continue to come in throughout Tuesday evening, and some on Wednesday as more states finish voting and officials start releasing their vote counts.
However, the first reported results will not necessarily mean that a winner has been announced.
Election officials release vote counts as ballots are processed, while news organisations such as the Associated Press analyse the results and determine when a race can be called.
Closely contested races could take hours, or even days, to call. It might not be immediately clear which party will control Congress.
Voters can cast their ballots by mail, early or in person on election day, which is Tuesday.
Many mail, provisional and other ballots are counted after election night, which is why tallies can take a few days, or even weeks, to finalise.
Senate Democrats need a net gain of four seats to reach a majority. House Democrats need three seats for a majority.
Here are a few key races to watch as the two parties go head-to-head:
