Super Tuesday is the biggest day in the presidential primary election season. This year, 13 states and one territory are participating.

The list includes Alabama, Alaska, Arkansas, Colorado, Georgia, Massachusetts, Minnesota, Oklahoma, Tennessee, Texas, Vermont, Virginia, Wyoming and American Samoa.

Super Tuesday happens on March 1. Polls close in most states at 7 p.m. or 8 p.m. ET, but results will still be coming in the next day. Republican caucusing in Alaska will continue until midnight ET. Here are the closing times for individual states:

7 p.m. ET: Georgia, Vermont, Virginia

8 p.m. ET: Alabama, Massachusetts, Oklahoma, Tennessee

8:30 p.m. ET: Arkansas

9 p.m. ET: Texas; Colorado and Minnesota caucuses begin

How does Super Tuesday work?

Each state handles the voting process differently. Some are primaries, which are run by the states. Others are caucuses, which are typically put on by the state parties.

A primary election is a simple secret-ballot vote administered by a state or local government. A caucus, by contrast, is run by the state-level political party. It involves some element of party activists convincing one another to join their preferred candidate.

Both Republicans and Democrats are holding their respective primaries on Super Tuesday in these states: Alabama, Arkansas, Georgia, Massachusetts, Oklahoma, Tennessee, Texas, Vermont, and Virginia.

Republicans and Democrats are holding caucuses in Colorado and Minnesota. Additionally, Republicans are holding caucuses in Alaska and Wyoming. Democrats hold their caucuses in American Samoa.

On the Republican side, five remaining candidates will participate in Super Tuesday. This include Donald Trump, Florida Sen. Marco Rubio, Texas Sen. Ted Cruz, Ohio Gov. John Kasich and retired neurosurgeon Ben Carson.

On the Democratic side, former Secretary of State Hillary Clinton will face off against Vermont Sen. Bernie Sanders.

While the polling varies by state, Trump and Clinton both look to be leading in a number of states. For Republicans, Trump looks to be leading in Virginia, Georgia, Oklahoma and Vermont. As for Texas, Cruz leads in some polls while Trump leads in others.

On the Democratic side, Clinton leads in most states that will vote on Super Tuesday. She is up by double digits in Texas, Virginia, Georgia, Arkansas and Alabama, according to recent polling. Sanders leads big in his home state of Vermont. He’s close or slightly ahead of Clinton in Massachusetts and Oklahoma, as per the reports of CBS News and The Huffington Post.