[Updated at 3:36 p.m. ET] Politicians are beginning to weigh in with their views on Twitter.
Perhaps no surprise, but House Democratic Leader Nancy Pelosi has high praise for Obama's announcement.
Democratic Rep. Matt Cartwright from Pennsylvania hit on one of the specifics Obama spoke about: Business.
And Republican Sen. John McCain, one of the senators who hammered out the bipartisan Senate proposal, tweeted a statement that he appreciated Obama's support of a bipartisan solution.
But he also noted, "The road ahead will be not be easy," but he is "cautiously optimistic" Democrats and Republicans can find common ground.
Republican Sen. Jeff Flake, also a member of the group behind the bipartisan Senate proposal, made clear where he thinks Obama differs from the senators:
[Updated at 3:30 p.m. ET] President Obama has done his part by beginning the conversation. Soon it will be time to wrangle over the specifics.
The White House has put out a fact sheet outlining the key principles motivating his overhaul of immigration and the areas he intends to focus on.
[Updated at 3:27 p.m. ET] CNN's chief political analyst Gloria Borger believes Obama's efforts have a better chance of succeeding than President George W. Bush and Sen. Ted Kennedy's attempts because there is more consensus that something needs to be done about immigration.
One question will dominate the debate, she said.
"How do you judge whether the borders are secure? That’s going to be a very big question as the senators try to map this out."
[Updated at 3:20 p.m. ET] A tweet from the president's account a few minutes ago has already been retweeted hundreds of times.
[Updated at 3:18 p.m. ET] Emory University law professor Polly Price told CNN there has been one flaw in American enforcement policy.
"What it has not done in the past is track people who are leaving, so usually they don’t know if someone here on a temporary visa has overstayed that visa," she said.
"It’s terribly important that there be an emphasis on enforcement," she added, but it's not been lacking under this administration.
Obama has deployed more enforcement than any previous president, but she suspects he'll expend some political capital to make sure immigrants have a pathway to citizenship, she said.
[Updated at 3:16 p.m. ET] Here's an early response from a Republican in the House of Representatives, which of course will play a key role if there is to be new legislation.
Rep. Lou Barletta, R-Pennsylvania, a critic of the Obama proposals, said we need to deal with the issue of visas and border security. Creating a path to citizenship before you deal with those issues is sending the wrong message.
“We’re talking about replacing the carpet when we still have a hole in the roof,” he said.
He further said he believes this is a political solution more than a practical one and estimates that it could cost as much as $2.7 trillion in things like unemployment, Medicare and and welfare to create such a pathway to citizenship.
[Updated at 3:08 p.m. ET] The president leaves the stage, now it's time for the analysis and reaction to what he said.
CNN's chief political analyst Gloria Borger said she believes Obama is playing good cop-bad cop, with his own left-leaning proposals being the bad cop and his Senate colleagues being the good cop. He's essentially saying, "If you don’t deal with them, you’re going to deal with me. Who would you rather deal with?" Borger said.
[Updated at 3:07 p.m. ET] "In the coming weeks, as the idea of reform becomes more real and the debate becomes more heated and there are folks who are trying to pull this thing apart, remember Alan and all those who share the same hopes and the same dreams. Remember this is not just a debate about policy, it’s about people. It’s about men and women and young people who want nothing more than the chance to earn their way into the American story," Obama said after telling one man's immigrant tale.
[Updated at 3:05 p.m. ET] Just as the president started speaking, Sen. Jeff Flake tweeted out a link to an editorial talking about the importance of border security - one of the key themes of the proposals by Flake and seven other senators yesterday.
[Updated at 3:02 p.m. ET] "I believe we are finally at a moment where comprehensive immigration reform is within our grasp," Obama said, but warning, "The closer we get, the more emotional this debate is going to become. Immigration has always been an issue that inflames passions."
[Updated at 2:58 p.m. ET] Now the plan. Obama says the principles are "straightforward."
The U.S. has to focus on enforcement, continuing to strengthen security on borders, and cracking down on businesses that knowingly hire illegal workers, Obama says.
Secondly, the country must deal with the 11 million immigrants here illegally. But for any plan to work, those immigrants have to realize “there is a pathway to citizenship.”
Part three is “bringing the legal immigration system into the 21st Century because it no longer reflects the reality of our time.” For instance, it shouldn’t take years for a legal immigrant’s family top qualify to join them in the U.S., he said.
This will help American be a “magnet for the best and the brightest all around the world," he said.
[Updated at 2:56 p.m. ET] Getting close to outlining his plan, Obama says there is a sense that changes should be done soon, so we can't let this get "bogged down in endless debate."
The ideas he’s proposing, he said, have been supported by Democrats like Ted Kennedy and Republicans like George W. Bush.
"You don’t get that match-up very often,” he said to chuckles from the audience.
[Updated at 2:55 p.m. ET] Cheers and applause greeted Obama's review of what he has already done, especially when he talked of the "Dreamers" - children brought to this country by their parents and who have done nothing wrong. He's speaking at Del Sol High School, which has a 54% Hispanic student body, according to U.S. News and World Report rankings.
[Updated at 2:50 p.m. ET] This isn’t just about illegal immigrants, Obama tells the room and the broader audience, but also about those who come to the U.S. to attend top universities to earn degrees in engineering and computer science, but after that, “there’s a good chance they’ll have to leave our country.”
Obama cited Intel and Instagram as examples of successful firms started by immigrants, and he said he wonders why we would tell today's immigrants graduating from American universities to go start their businesses abroad.
[Updated at 2:48 p.m. ET] Obama has the demeanor of a popular principal addressing a gathering of students. He's getting a good reception from the friendly audience.
[Updated at 2:46 p.m. ET] Obama praises the positive impact of immigrants, highlighting Google, Yahoo and other high-tech startups. He says one in four is started by immigrants.
It’s time to address “a system that’s holding us back rather than helping us grow our economy and strengthen the middle class.”
[Updated at 2:43 p.m.] "The differences are dwindling," the president says, calling immigration one of the “defining challenges of our time.”
"I am here today because the time has come for commonsense comprehensive immigration reform."
"Now is the time," he says, prompting shouts of "Si, se puede" – Spanish for "yes we can."
[Updated at 2:40 p.m. ET] The president has just taken the stage. In the audience, Obama tells us, are Homeland Security Secretary Janet Napolitano and Secretary of the Interior Ken Salazar.
[Posted at 1:45 p.m. ET] We still have some time before the president will speak but we're already beginning to get an idea of how the issue may be framed by the politicians.
Sen. Marco Rubio, who is one of the senators who revealed a bipartisan plan yesterday, spoke on the Senate floor about his concerns about the president's plans:
"In a few hours the president will give a speech in Nevada. And early press accounts concern me. I don’t want to turn this into a partisan thing so let me just say this – if this endeavor becomes a bidding war to see who can come up with the easiest, quickest and cheapest pathway to green card possible this thing is not going to go well folks. We now have a very common sense and reasonable set of principles and I hope what the president will say today is that he hopes that that process succeeds. But if his intentions are to trigger a bidding war to see who can come up with the easiest process, this is not a good start. But let’s give him the benefit of the doubt."
It may not be related, but we've just gotten the first excerpt from the White House about what the president will say:
"We need Congress to act on a comprehensive approach that finally deals with the 11 million undocumented immigrants who are in this country right now. The good news is that – for the first time in many years – Republicans and Democrats seem ready to tackle this problem together. Members of both parties, in both chambers, are actively working on a solution. And yesterday, a bi-partisan group of Senators announced their principles for comprehensive immigration reform, which are very much in line with the principles I’ve proposed and campaigned on for the last few years. At this moment, it looks like there’s a genuine desire to get this done soon. And that’s very encouraging."
Our colleagues with the Political Ticker break down what you can expect to hear from Obama today.
[Posted at 1:42 p.m. ET] President Obama is to speak in Las Vegas, Nevada, at 2:55 p.m. ET where he will lay the groundwork for his immigration overhaul - something he has spoken about passionately before being elected as well as during his presidency, but has never followed through on.
The president, who won a second term in part because of the support from Latino voters, is expected to lay out his vision and insist that now is the time to act when it comes to reform.
Obama's comments will come a day after a key group of bipartisan senators announced their own plan for immigration.
Republicans including Sen. John McCain, Sen. Marco Rubio, who is a rising star in the party and an expected 2016 presidential candidate, Sen. Lindsey Graham and Sen. Jeff Flake worked on the plan with Democratic Sens. Chuck Schumer, Dick Durbin, Robert Menendez and Michael Bennet.
The four "pillars" of the Senate plan are: