6061, is an act of the United States Congress which authorized and partially funded the construction of 700 miles (1,125 km) of fencing along the Mexican border.

The Act received bipartisan support.The Senate focused more on the effectiveness of a border fence, while the House debate included more objections to the closed-rule procedure that restricted changes.

"[2] An amendment introduced by Senator Kay Bailey Hutchison, Republican of Texas, was passed as part of the Consolidated Appropriations Act, 2008,[3] amending the law to read: "nothing in this paragraph shall require the Secretary of Homeland Security to install fencing, physical barriers, roads, lighting, cameras, and sensors in a particular location along an international border of the United States, if the Secretary determines that the use or placement of such resources is not the most appropriate means to achieve and maintain operational control over the international border at such location.

"[2] By April 2009, DHS had erected about 613 miles (985 km) of new pedestrian fencing and vehicle barriers along the southwest border from California to Texas.

[4] Delays frustrated some, such as Senator Jim DeMint, Republican of South Carolina, who in 2010 introduced legislation seeking to require completion of the 700-mile-long, double-layered fence.

(DHS had since 2007 begun "to shift its focus to erecting a 'virtual fence' along the 2,000-mile border, using sensors, cameras and other high-tech equipment to prevent illegal crossings".)

[14] A 2019 National Bureau of Economic Research paper by Dartmouth College and Stanford University economists found that the "total impact of the border wall expansion including all general equilibrium adjustments was to reduce the (long-run) number of Mexican workers residing in the United States by about 50,000, a decline of approximately 0.4%.

"[16] The study identified the most "at risk" species as the Arroyo toad (Anaxyrus californicus), California red-legged frog (Rana draytonii), black-spotted newt (Notophthalmus meridionalis), Pacific pond turtle (Clemmys marmorata), and jaguarundi (Puma yagouaroundi).

"[16] A paper by University of Pennsylvania political scientist Benjamin Laughlin estimates that the Secure Fence Act caused at least 1,000 additional deaths in Mexican regions adjacent to the U.S.-Mexican border.

[6] Trump's proposed wall—which he said would consist of 2,000 miles "of hardened concrete, and ... rebar, and steel" across the entire southern border[20] would be much more extensive than the fencing built under the 2006 act.

Experts doubt that the border wall proposed by Trump would actually significantly reduce illegal immigration, or have any benefits commensurate with the anticipated high cost of construction, estimated to be billions of dollars.

[22][23] Trump's demand for Congress to appropriate $5.7 billion for the wall resulted in the 2018–19 United States federal government shutdown, which lasted for 35 days.