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

As a result, this is effectively former U.N. Ambassador Nikki Haley’s last shot to slow former President Donald Trump’s path towards 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 criss-crossing the country in the final days ahead of March 5 to meet as many voters as possible.

Trump will be entering the week coming off of wins in Haley’s home state of South Carolina, winning 60% of the vote, and Michigan, where he secured 70% of the vote. While Trump does lead on delegate count and votes, having won every primary 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. States holding primary elections that conclude on March 5 include: Alabama, Alaska, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont and Virginia. Democrats in the U.S. territory American Samoa will also be caucusing and Democrats in Iowa will release the results of their presidential preference caucus. (The American Samoa Republican presidential caucus will be held on Friday.)

Get caught up on delegate counts that each Republican presidential candidate has 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.

Who are people voting for on Super Tuesday?

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

But there are candidates who have dropped out who 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 the state’s 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. There are nine Democratic candidates looking to be Cruz’s opponent in the fall.
• Alabama will be voting under a new congressional map that opened up a new district in the southwest corner of the state. Last fall, a federal court decided on Alabama’s new congressional map that is likely to result in a Democratic member of the U.S. House.