The executive actions that President Obama announced Thursday are wide-reaching and complicated. Even the top-line numbers — such as how many people will be affected — are tough to pin down, because they are based on estimates of a population that Obama himself has said is living the shadows.

NPR's Scott Horsley has outlined many of the details. We've been sifting through memos and fact sheets to drill a bit deeper. Here's what we've come up with:

-- How Many People Are Affected?

The White House estimates that up to 5 million immigrants could be affected by these actions, 4 million of whom are here illegally.

The vast majority are likely to be parents with children who are U.S. citizens or hold a green card, according to the White House. They will be shielded temporarily from deportation. Another big group falls under the expansion of a 2012 executive action called DACA, or Deferred Action for Childhood Arrivals, which defers deportation for people brought into the country illegally as children.

The Pew Research Center projects that 3.7 million people here illegally may be affected and the Migration Policy Institute puts the number at 4 million.

-- Why Do I Keep Hearing Different Numbers?

These are projections, and small tweaks can yield different numbers. Pew, for example, only counts parents who are living with their children, while the White House may use a different method.

And to add another wrinkle, the Migration Policy Institute says media coverage of the executive actions could spur many young people — who were already eligible — to apply for deferred action and a work permit under DACA. Remember, it is estimated that about 60 percent of those young immigrants actually applied for deferred action.

So if you include those who have not yet applied, the MPI says Obama's executive action could affect as many as 5.2 million people.

-- Who's Receiving Relief And What Do They Get?

Two broad categories are the most important:

If they have lived in the U.S. for at least five years, the parents of children who are either U.S. citizens or hold a green card are entitled to deferred action and a three-year work permit. The parents can also apply for a Social Security card, and will be entitled to Social Security benefits. They may also be eligible for the Earned Income Tax Credit — a tax subsidy for low-wage workers. But they are ineligible for insurance subsidies and other benefits under the Affordable Care Act

The executive actions also expanded protection to include any children who were brought to this country illegally before Jan. 1, 2010. (With DACA, the president deferred the deportation of those who were born after 1981 and entered the country before June 15, 2007.)

Applicants in these two groups will have to pay any administrative fees and submit to a background check.

There is a third category of people who will be affected. Broadly, the executive actions will make it easier for professionals or "talented entrepreneurs" to remain in the country. We have not seen a reliable estimate for how many people are included in this category.

-- Do They Get Legal Status?

No. The executive actions do not provide a path to a green card or U.S. citizenship. As President Obama said in his address, only Congress can do that.

-- Can Immigrants Travel Out Of The Country?

The administration is clarifying the way it deals with what it calls "advance paroles." Essentially, the Department of Homeland Security is saying that the U.S. Citizenship and Immigration Services — at its discretion, and case by case — can grant those immigrants permission to travel out of the country and then come back in.

-- What About Enforcement?

Another part of Obama's executive actions sends more resources to the border and prioritizes the deportation of criminals and recent arrivals.

There are slightly more than 11 million undocumented immigrants estimated to be living in this country. While the remaining 6 million won't receive a work permit, the government says it will not actively try to deport them if they have not been convicted of a crime.

What's more, Obama ended Secure Communities, a program which linked local and federal authorities in order to identify and detain undocumented immigrants who came in contact with police, even just as a result of a traffic stop.

In its place is something dubbed Priority Enforcement Program. Local and federal authorities will still share information, but Immigration and Customs Enforcement will only ask local authorities to hold immigrants who have been convicted of a serious crime.

-- When Does All This Start?

The best answer we have is from U.S. Citizenship and Immigration Services, which says, "Some initiatives will be implemented over the next several months, and some will take longer."

Update at 1:22 p.m. ET. On Dec. 2: About Benefits:

We've updated this post with new information regarding social security benefits. At the time the post was written, the White House said immigrants protected under Obama's plan would not be entitled to social security benefits.

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