This year, all 435 seats in the US House of Representatives, as well as 35 seats in the Senate are being contested.
Republicans have taken a sizable lead in the race to control the US House of Representatives, with incomplete results showing a significant lead over Democrats.
In all, Republicans have won so far 199 seats in the chamber, compared to 172 for Democrats, according to the latest tally.
While the margins are likely to change as results are tabulated, a forecast from the New York Times newspaper puts chances of Republican control of the House at 74 percent.
Democrats have just a 26 percent chance of retaining their hold on the chamber. Most analysts widely predicted a Republican takeover of the House, though the Senate remains a topic of intense speculation.
This year, all 435 seats in the House are up for election, compared to 35 seats in the Senate. The vast majority of Senate seats - 21 - are held by Republican incumbents.
But the Senate is currently evenly split between Republicans and Democrats, greatly increasing the importance of each seat for both parties.
Tight Senate race
With Tuesday evening quickly winding down in the US, the tight race for the Senate is continuing.
Republicans so far won 47 seats compared to 46 by Democrats.
There are about 10 Senate races across the country that could prove pivotal in determining whether Republicans or Democrats lay claim to the chamber, including in Georgia, where incumbent Senator Raphael Warnock is trailing his Republican opponent, former American football star Herschel Walker, by 0.6 percent, according to RealClearPolitics.
Results in any number of races are unlikely to be known on Election Day, and tightly watched races could take days to determine.
Some states also have a significant backlog of absentee or mail-in votes which, depending on the local rules, cannot begin to be counted before Election Day.
While international attention will remain focused on top-line congressional races, further down the ballot, voters will weigh in on a series of state and local campaigns, from governors' races to ballot initiatives such as marijuana legalization, and more mundane but nonetheless important races for local offices.
This year, all 435 seats in the House of Representatives, as well as 35 seats in Senate are being contested.
Most analysts are predicting Republicans will gain control of the House, but the fate of Senate remains a topic of intense speculation.
READ MORE: Explained: 2022 US midterm elections