President Trump has promised to build his "giant wall," but it will take a lot of help to make it a reality.
Trump said he will lay out his plans Wednesday to build a border wall along the nation's southwest border with Mexico, a campaign pledge that became so popular with his supporters that they regularly chanted "Build that wall" at rallies.
Now that he's in the White House, Trump can make some moves on his own and possibly start construction, but finishing the wall will require a big assist from Congress.
Here's a look at some of the basics behind the border wall.
The U.S. "border wall" is really a collection of walls, fences and other barriers that currently cover 652 miles of the 1,954-mile border with Mexico, according to the Government Accountability Office.
The wall is strongest along parts of the border that have large populations on both sides, such as San Diego and Tijuana.
Each city runs right up to the border, so Department of Homeland Security officials have built up double and triple layers of fencing for 14 miles starting in the Pacific Ocean and heading east.
In other, more desolate parts of the border, there are only single fences or a variety of barriers, including iron vehicle barriers that people can easily walk past.
Most areas have no fencing, but some are nearly impossible to cross, from the widest sections of the Rio Grande to deep canyons and treacherous mountains.
Predictions have varied widely, but it will be expensive.
Trump took his own stab at the figure in February, telling MSNBC he could finish the wall for $8 billion. But most other estimates are far higher.
In 2015, Border Patrol officials said during a Senate hearing that the current 652 miles of wall had cost $2.3 billion. But that does not include increased costs for building across more difficult terrain or building the wall higher, as Trump has said he would do.
The Bernstein Research group conducted a study in July and estimated the total costs to be between $15 and $25 billion.
It's possible that Trump could kick-start some construction on his own.
When Congress passed the Secure Fence Act of 2000, it provided approval for up to 700 miles of fencing. With 652 miles currently built, that means Trump could try and build the remaining miles on his own.
But to build the additional 1,200 miles, he would need funding from Congress. GOP leaders in both chambers have said they would help Trump secure the border, but have not committed to funding the billions Trump needs.
Trump has repeatedly said that he would get Mexico to pay for the construction of the wall.
He said they would do so through a combination of factors, including increased fees and taxes to cross the southwest border, and withholding remittances that Mexican nationals in the U.S. send back to their families in Mexico.
He could need congressional help there as well, as Congress would need to create a legal mechanism to withhold that much money. The plan could also face legal challenges.
But Trump recently changed his stance, tweeting last month that the U.S. "will be paid back by Mexico later!"