Voters in 16 states and one territory will make their voices heard Tuesday in the biggest primary election day of the 2024 cycle. Also known as Super Tuesday, this biggest single primary contest day will result in over a third of delegates assigned to determine the Republican presidential nominee.

As a result, this is effectively former U.S. Ambassador to the U.N. Nikki Haley's last shot to slow former President Donald Trump's path toward nomination. Ahead of the mammoth election night, Haley's campaign launched a seven-figure national cable and digital ad buy to run through at least Tuesday in hopes of winning over voters. Her campaign has also been crisscrossing the U.S. in the final days ahead of March 5 to meet as many voters as possible.

Trump will be entering the week coming off wins in Haley's home state of South Carolina , winning 60% of the vote there, and Michigan , where he secured about 70% of the vote. While Trump does lead on delegate count and votes, having won every primary but one thus far, Haley is still securing a third of voters, which could be an eventual concern for Trump in what's shaping up to be a general election rematch with President Biden on Nov. 5.

Super Tuesday is not the end of the primary season. The remaining states will vote through the summer and fall on their primary slates. Republicans will gather in July in Milwaukee for their convention to officially nominate the GOP candidate for the general election, and Democrats will gather in Chicago in August to select their candidate.

What is Super Tuesday, and which states are voting?

It's known as Super Tuesday because that's when votes will be tallied from the most states at once in the presidential primary. The states holding primary elections that conclude on March 5 are Alabama, Alaska, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont and Virginia. Democrats in the U.S. territory of American Samoa will also be caucusing, and Democrats in Iowa will release the results of their presidential preference caucus. (American Samoa's Republican presidential caucus will be held on Friday.)

Get caught up on the delegate count of each Republican presidential candidate with NPR's tracker.

When will we know results?

Because voting will be taking place across six time zones, it may take hours and days to determine the winners of delegates and the winning party candidates to move onto the general elections for governor, state legislature and congressional seats.

In some states, it may take longer to count mail-in ballots. For example, in California, mail-in ballots must be postmarked by March 5 and received by county election offices by March 12 , meaning not all votes will be tallied on Tuesday, especially for races with close margins.

Final polls will start closing at 7 p.m. ET — in Virginia and Vermont.

Whom are people voting for on Super Tuesday?

Really basically, Trump and Haley will be the options on the Republican presidential primary ballot. President Biden will be the option for Democrats, though Democratic Rep. Dean Phillips of Minnesota is still running a long shot challenge.

But candidates who have dropped out will still appear on the ballot in some places because of the rules to get on a ballot in each state. So, while voters might be able to vote for entrepreneur Vivek Ramaswamy or businessman Ryan Binkley on the Republican side, those candidates are not in the race.

As for third-party options like Robert F. Kennedy and professor Cornel West , those candidates will not be on the major-party primary ballots because they are not running on a major-party ticket.

While most eyes will be on the presidential race, particularly for the Republicans, voters will also be making decisions on their final slate of candidates in Senate, House and governors races that can determine political control of Congress and states for the next two to four years.

  • California voters will get their say on the Democratic nominee for the Senate seat long held by the late Sen. Dianne Feinstein, now occupied by Sen. Laphonza Butler. Because it is a solidly blue seat, the primary will likely signal the front-runner for the election in November, though it may take several days to determine the winner due to mail-in voting counts.

  • North Carolina votes in a high-stakes gubernatorial race. The state legislature is currently controlled by Republicans, and Democratic Gov. Roy Cooper has reached his term limit — leaving an open seat.

  • Texas will pick the Democratic challenger to Sen. Ted Cruz, who is seeking a third term. Nine Democratic candidates are looking to be Cruz's opponent in the fall.

  • Alabama will be voting under a new congressional map that opened a new district in the state's southwest corner. Last fall, a federal court decided on Alabama's new congressional map, which is likely to result in a Democratic member of the U.S. House.

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    Corrected: March 04, 2024
    An earlier version of this story incorrectly said Donald Trump has won every Republican presidential primary election thus far. In fact, Nikki Haley won the Republican presidential primary election in the District of Columbia.