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President Biden on Wednesday will give a primetime address to a joint session of Congress, marking the biggest speech of his presidency so far and giving him the opportunity to lay out his agenda for the rest of his time in office. 

Biden's address also comes on the eve of his 100th day in office, giving him the chance to reflect on what's been a busy few months, including a coronavirus stimulus, a subsequent spending plan that he proposed and partisan battles over immigration. 

Biden is also expected to lay out a proposal for yet another spending bill, which he will call the "American Families Plan." This will be a follow-up to his "American Jobs Plan," which the White House has sold as an infrastructure bill, and the "American Rescue Plan," which was a stimulus aimed at providing relief from the coronavirus pandemic. 

Here's what to know about Biden's address to a joint session of Congress.

President Biden speaks about COVID-19, on the North Lawn of the White House, Tuesday, April 27, 2021, in Washington. (AP Photo/Evan Vucci)

President Biden speaks about COVID-19, on the North Lawn of the White House, Tuesday, April 27, 2021, in Washington. (AP Photo/Evan Vucci) (AP Photo/Evan Vucci)

When is it? 

Biden will speak at 9 p.m. You can watch the address live on Fox News Channel and FoxNews.com. 

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Where is it? 

Biden's address will take place in the House chamber in the U.S. Capitol, where such addresses are usually held. 

Why is it not the State of the Union? 

Presidents who recently assumed office deliver an address to a joint session of Congress rather than a State of the Union. This is because they have not been in office for very long. 

Biden's speech, however, is taking place later than most new presidents in recent years. Former President Trump, for example, spoke on Feb. 28, 2017. 

The delay is largely attributable to the security situation at the Capitol after the Jan. 6 riot and the coronavirus pandemic. 

Why is the speech happening? 

The president is required by the Constitution to "from time to time give to the Congress Information on the State of the Union."

The speech is not a requirement. Some past presidents have given their updates in writing. President Woodrow Wilson brought back the tradition of giving a speech to Congress in 1913 after no president had done the same since Thomas Jefferson. 

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Calvin Coolidge was the first president to have his address to Congress broadcast on the radio, and Franklin Delano Roosevelt was the first to call it the "State of the Union."

President Harry Truman was the first to deliver the address on television, and Lyndon Johnson the first to deliver it in primetime in 1964. 

Who will be there? 

Vice President Kamala Harris and House Speaker Nancy Pelosi, D-Calif., will be the most prominently visible attendees, sitting behind Biden in the chamber, as is traditional for such addresses. 

Many members of Congress will not be able to be at the speech, however, due to coronavirus protocols. 

Rep. Liz Cheney, R-Wyo., the House Republican Conference chair, speaks with reporters following a GOP strategy session on Capitol Hill in Washington, Tuesday, April 20, 2021. Cheney will be at President Biden's address to a joint session of Congress. (AP Photo/J. Scott Applewhite)

Rep. Liz Cheney, R-Wyo., the House Republican Conference chair, speaks with reporters following a GOP strategy session on Capitol Hill in Washington, Tuesday, April 20, 2021. Cheney will be at President Biden's address to a joint session of Congress. (AP Photo/J. Scott Applewhite)

Among the Republicans who will be there are Senate Minority Leader Mitch McConnell, R-Ky., and House Minority Leader Kevin McCarthy, R-Calif. Sens. Ted Cruz, R-Texas, and Rick Scott, R-Fla., will also be in attendance. 

Some House members who will be there are Rep. Liz Cheney, R-Wyo., and Rep. Lauren Boebert, R-Colo.

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House Minority Whip Steve Scalise, R-La., however, will not be at the event. Nor will Sens. Marco Rubio, R-Fla., Josh Hawley, R-Mo., or Tom Cotton, R-Ark. 

Among Democrats, Sens. Dick Durbin, D-Ill., Patrick Leahy, D-Vt., Dianne Feinstein, D-Calif., Amy Klobuchar, D-Minn., Chris Coons, D-Del., John Hickenlooper, D-Colo., Jon Ossoff., D-Ga., Raphael Warnock, D-Ga., and several others will attend. There will be 35 Democratic senators at the address in all – well over half of their caucus. 

Chief Justice John Roberts will be the only member of the Supreme Court present. Secretary of State Antony Blinken and Defense Secretary Lloyd Austin will be the only Cabinet members present. 

There are only expected to be about 200 people in the House chamber total, including 80 House members and 60 senators. 

Normally, there are about 1,600 people at presidential addresses like this one. 

What's in the American Families Plan? 

The plan includes universal "high-quality preschool" for 3- and 4-year-old children, according to a senior administration official, and two years of free community college for all Americans. 

The legislation will also include new funding for historically Black colleges and universities, teacher training, expanded child tax credits and a national paid-leave program. 

The plan is expected to cost $1.8 trillion. 

Security is being stepped up

The U.S. Secret Service, Capitol Police, Metropolitan Police Department, U.S. Park Police and other agencies will provide security for what will be a very locked-down Capitol Complex on Wednesday. 

Starting at 7 p.m., sections of a number of streets will be closed off, including Pennsylvania Avenue NW and Constitution Avenue NW. Seventeen total streets will see at least some level of closure Wednesday. 

People with event credentials and with congressional IDs will be the only people allowed on the Capitol grounds starting at 7 p.m. Vehicles will be subject to similar restrictions. 

The security situation will be closely watched after the attack on the Capitol on Jan. 6.

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What are the mask rules? 

House members will be required to wear masks on the House floor, according to a rule imposed by Pelosi on Jan. 4. House members will also be subject to a security sweep, also per House rules.

But it's not clear how those rules will apply to senators or members of Biden's Cabinet.

Senate Majority Leader Chuck Schumer, D-N.Y., was stumped when asked what the requirements for senators are going to be on the House floor, as House rules technically don't apply to senators. 

U.S. Sen. Tim Scott, R-S.C., poses before a meeting with Justice Amy Coney Barrett during her confirmation process on Sept. 29, 2020, in Washington, D.C. Scott will deliver the Republican response to President Biden's address to a joint session of Congress on Wednesday. Barrett will not be in attendance -- Chief Justice John Roberts is the only Supreme Court justice invited to the speech. (Bonnie Cash-Pool/Getty Images)

U.S. Sen. Tim Scott, R-S.C., poses before a meeting with Justice Amy Coney Barrett during her confirmation process on Sept. 29, 2020, in Washington, D.C. Scott will deliver the Republican response to President Biden's address to a joint session of Congress on Wednesday. Barrett will not be in attendance -- Chief Justice John Roberts is the only Supreme Court justice invited to the speech. (Bonnie Cash-Pool/Getty Images)

Who is giving the GOP response to Biden's speech? 

Sen. Tim Scott, R-S.C., will deliver the Republicans' response to Biden. He was chosen for the job by McConnell and McCarthy.

"Sen. Tim Scott is not just one of the strongest leaders in our Senate Republican Conference. He is one of the most inspiring and unifying leaders in our nation," McConnell said. "Nobody is better at communicating why far-left policies fail working Americans."

"I'm excited and honored for this opportunity to address the nation," Scott said in a statement. "We face serious challenges on multiple fronts, but I am as confident as I have ever been in the promise and potential of America. I look forward to having an honest conversation with the American people and sharing Republicans’ optimistic vision for expanding opportunity and empowering working families."

Who will deliver the left-wing response to Biden's speech? 

Rep. Jamaal Bowman, D-N.Y., a new member of the left-wing "Squad" in the House, will deliver the Working Families Party's response to Biden's speech. 

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"Honored to deliver the response to President Biden's address next week with @WorkingFamilies. Let's go!" Bowman said in a tweet. 

The Working Families Party is a progressive party that is often a thorn in the side of establishment Democrats. But it often works with left-wing members of the party who otherwise are loyal Democrats. 

Bowman is not expected to be exclusively critical of Biden, and as recently as Tuesday lauded Biden's "American Families Plan" as "an opportunity to rebuild our communities for our collective wellbeing." But he is expected to aim to move Biden and the rest of the Democratic Party to the left. 

Fox News' Chad Pergram, Edmund DeMarche and Marisa Schultz contributed to this report.