A border wall is being built along portions of the Mexico–United States border in an attempt to reduce illegal immigration to the United States from Mexico. The barrier is not a continuous structure but a series of obstructions variously classified as "fences" or "walls".Chaichian, Mohammad. 2014. Empires and Walls: Globalization, Migration, and Colonial Domination (Brill, pp. 175–235)

Between the physical barriers, security is provided by a "virtual fence" of sensors, cameras, and other surveillance equipment used to dispatch United States Border Patrol (USBP) agents to suspected migrant crossings. In May 2011, the Department of Homeland Security (DHS) said it had of barriers in place. A total of of new primary barriers were built during Donald Trump's first presidency, dubbed the "Trump Wall", though President Trump had repeatedly promised a "giant wall" spanning the entire border and that Mexico would "pay for the wall". The national border's length is , of which is the Rio Grande and is on land.

President Joe Biden signed an executive order on his first day of office, January 20, 2021, which ordered a pause in all construction of the border wall no later than January 27, 2021. By December 2021, many contracts had been cancelled. On July 28, 2022, the Biden administration announced it would fill four wide border wall gaps in Arizona near Yuma, an area with some of the busiest corridors for illegal crossings. In October 2023, President Biden announced that he was restarting border wall construction on some parts of the border due to the surge of migrant crossings, constructing an additional of border wall.

In January 2025, re-elected president Trump pledged to finish the border wall during his second term. The amount of existing Wall (prior to 1/20/2025) that met USBP operational requirements was ~644 miles of Primary Wall and ~75 miles of Secondary Wall. On October 10, 2025, the initiative was officially designated as a "Smart Wall", with an interactive Smart Wall Map Page, to reflect the layers of "System Attributes" and other detection technology that would be incorporated into the design. In a May 2026 interview, DHS secretary Markwayne Mullin stated that he expected the Primary Wall to be completed by April or June 2027 with the Secondary Wall and other components to be completed before Trump left office. In a June 11, 2026 interview, Customs and Border Protection (CBP) commissioner Rodney S. Scott stated that CBP was building about 6 miles of wall per week, that he made a commitment to President Trump that the Primary Wall would be completed by the end of 2027 and that the entire system would be completed by July 2028. On September 18, 2026, it was reported that CBP was constructing an average of 12 miles of barrier per week.

CBP publishes construction progress updates to its Smart Wall Map Page on a weekly basis. , CBP has completed: 81.6 miles of 626 miles of planned new Primary Border Wall; 43.5 miles of 137 miles of planned replacement Primary Border Wall; 0 miles of 183 miles of planned Vehicle Barrier; 47.3 miles of 533 miles of planned Waterborne Barrier System; and 84.0 miles of 578 miles of planned Secondary Border Wall.

Description The border between Mexico and the U.S. traverses a variety of terrain, including urban areas and deserts. The border from the Gulf of Mexico to El Paso, Texas, follows the Rio Grande, a natural barrier. The barrier is on both urban and uninhabited sections of the border, where the most illegal crossings and drug trafficking have been observed in the past. These urban areas include San Diego, California, and El Paso, Texas.Sapp, Lesley (July 2011). Apprehensions by the U.S. Border Patrol: 2005–2010. Office of Immigration Studies, United States Department of Homeland Security (Washington, D.C.) Retrieved November 18, 2011, The fencing includes a steel fence varying in height between that divides the border towns of Nogales, Arizona, in the U.S. and Nogales, Sonora, in Mexico.Peter Holley, "Trump proposes a border wall. But there already is one, and it gets climbed over", Washington Post (April 2, 2016).

97% of border apprehensions (foreign nationals caught in the U.S. illegally) by the Border Patrol in 2010 occurred at the southwest border. The number declined 61% from 1,189,000 in 2005 to 723,842 in 2008 to 463,000 in 2010. The decrease in apprehensions is the result of numerous factors, including changes in U.S. economic conditions and border enforcement efforts. Border apprehensions in 2010 were at their lowest level since 1972. Total apprehensions for 2017, 2018, and 2019 were 415,517, 521,090, and 977,509, respectively. And while the barrier is along the border with Mexico, 80% of those apprehended are not Mexican.

As a result of the barrier, the number of people trying to cross in areas that have no fence, such as the Sonoran Desert and the Baboquivari Mountains in Arizona, has increased. Such immigrants must cross 50 miles (80 km) of inhospitable terrain to reach the first road, which is in the Tohono Oʼodham Indian Reservation.One Nation, Under Fire High Country News, February 19, 2007.

Geography The Mexico–U.S. border stretches from the Pacific Ocean in the west to the Gulf of Mexico in the east. Border states include the Mexican states of Baja California, Sonora, Chihuahua, Coahuila, Nuevo León, and Tamaulipas and the U.S. states of California, Arizona, New Mexico, and Texas.

+ Border by U.S. state U.S. state Border length Mexican states California Baja California Arizona Baja California, Sonora New Mexico Sonora, Chihuahua Texas Chihuahua, Coahuila, Nuevo León, Tamaulipas Total

History

Origins Territorial exchanges in the Mexican–American War (1846–1848) and the Gadsden Purchase (1853) largely established the current U.S.–Mexico border. Until the early 20th century, the border was open and largely unpatrolled, with only a few "mounted guards" patrolling its length. But tensions between the U.S. and Mexico began to rise with the Mexican Revolution (1910) and World War I, which also increased concerns about weapons smuggling, refugees and cross-border espionage. The first international bridge was the Brownsville & Matamoros International Bridge, built in 1910. The first barrier built by the U.S. (a barbed-wire fence to prevent the movement of cattle across the border) was built in Ambos Nogales between 1909 and 1911, and was expanded in 1929 with a "six foot–high chain-link fence". The first barrier built by Mexico was likely a -tall wire fence built in 1918 explicitly for the purpose of directing the flow of people, also in Ambos Nogales. Barriers were extended in the following decades and became a common feature in border towns by the 1920s. In the 1940s, the U.S. Immigration and Naturalization Service built chain-link barriers along the border.

The U.S. Congress approved a $4.3 million request by Immigration and Naturalization Service, in 1978, to build a fence along the border to replace an existing fence near San Ysidro, California, and El Paso, Texas, and then build an additional of new fence. Anchor Post Products was contracted to build the new fence in a project inherited from Richard Nixon, who was the first president to propose building a border fence. The proposed construction received press coverage after the company's George Norris, described the fence as a "razor-sharp wall", leading to negative responses in Mexico. The proposed wall, dubbed the "Tortilla Curtain" by critics, was condemned by Mexican politicians such as then-president José López Portillo, and it was raised as an issue during President Jimmy Carter's state visit to Mexico in February 1979. Fencing was ultimately constructed, but had a limited length and did not have razor wire.

U.S. president George H. W. Bush approved the initial 14 miles (22.5 km) of fencing along the San Diego–Tijuana border. In 1993, President Bill Clinton oversaw initial border fence construction which was completed by the end of the year. Starting in 1994, further barriers were built under Clinton's presidency as part of three larger operations to taper transportation of illegal drugs manufactured in Latin America and immigration: Operation Gatekeeper in California, Operation Hold-the-LineMcPhail, Weldon, Assistant Director, Administration of Justice Issues, Dennise R. Stickley, Evaluator, David P. Alexander, Social Science Analyst: Washington, DC, Appendix I:1; Michael P. Dino, Evaluator-in-Charge, James R. Russell, Evaluator: LA Regional Office, Appendix I:2; "Border Control: Revised Strategy Is Showing Some Positive Results" . Subcommittee on Information, Justice, Transportation and Agriculture, Committee on Government Operations, House of Representatives, December 29, 1994. in Texas, and Operation Safeguard in Arizona. Clinton signed the Illegal Immigration Reform and Immigrant Responsibility Act of 1996, which authorized further barriers and the reinforcement of the initial border fence. The majority of the border barriers built in the 1990s were made out of leftover helicopter landing mats from the Vietnam War. Unlike the WWII-era Marston Mats, the M8A1 used for border barrier lacked circular holes. The panels were flipped vertically and interlocked to become fencing. However, the solid, opaque wall presented susbtantial agent safety risks. Also, the mats were susceptible to under-digging, scaling and rusting over time.

Bush administration (2001–2009)

The Real ID Act, signed into law by President George W. Bush on May 11, 2005, attached a rider to a supplemental appropriations bill funding the wars in Iraq and Afghanistan, which went into effect in May 2008:Notwithstanding any other provision of law, the Secretary of Homeland Security shall have the authority to waive all legal requirements such Secretary, in such Secretary's sole discretion, determines necessary to ensure expeditious construction of the barriers and roads.

In 2005, there were of fencing along the border. In 2005, the border-located Laredo Community College obtained a fence built by the United States Marine Corps. The structure led to a reported decline in border crossings onto the campus. U.S. representative Duncan Hunter of California proposed a plan on November 3, 2005, calling for the construction of a reinforced fence along the entire United States–Mexico border. This would also have included a border zone on the U.S. side. On December 15, 2005, Hunter's amendment to the Border Protection, Anti-terrorism, and Illegal Immigration Control Act of 2005 (H.R. 4437) passed in the House, but the bill did not pass the Senate. This plan called for mandatory fencing along of the -long border. On May 17, 2006, the U.S. Senate proposed the Comprehensive Immigration Reform Act of 2006 (S. 2611), which would include of triple-layered fencing and a vehicle fence, but the bill died in committee.

Secure Fence Act of 2006

The Secure Fence Act of 2006, signed into law on October 26, 2006, by President George W. Bush authorized and partially funded the potential construction of of physical fence/barriers along the Mexican border. The bill passed with supermajorities in both chambers. Secretary of Homeland Security Michael Chertoff announced that an eight-month test of the virtual fence he favored would precede any construction of a physical barrier.