United States Department of Homeland Security in the context of Computer security

Science, technology, engineering, and mathematics (STEM) is an umbrella term used to group together the related technical disciplines of science, technology, engineering, and mathematics. It represents a broad and interconnected set of fields that are crucial for innovation and technological advancement. These disciplines are often grouped together because they share a common emphasis on critical thinking, problem-solving, and analytical skills. The term is typically used in the context of education policy or curriculum choices in schools. It has implications for workforce development, national security concerns (as a shortage of STEM-educated citizens can reduce effectiveness in this area), and immigration policy, with regard to admitting foreign students and tech workers.

There is no universal agreement on which disciplines are included in STEM; in particular, whether or not the science in STEM includes social sciences, such as psychology, sociology, economics, and political science. In the United States, these are typically included by the National Science Foundation (NSF), the Department of Labor's O*Net online database for job seekers, and the Department of Homeland Security. In the United Kingdom, the social sciences are categorized separately and are instead grouped with humanities and arts to form another counterpart acronym HASS (humanities, arts, and social sciences), rebranded in 2020 as SHAPE (social sciences, humanities and the arts for people and the economy). Some sources also use HEAL (health, education, administration, and literacy) as the counterpart of STEM.

Mass murder is the violent crime of killing a number of people, typically simultaneously or over a relatively short period of time and in close geographic proximity. A mass murder typically occurs in a single location where one or more persons kill several others. Data suggests that approximately 30% of mass murderers die in the act.

In the United States, Congress defined mass murders as the killing of three or more persons during an event with no "cooling-off period" between the homicides. The Investigative Assistance for Violent Crimes Act of 2012, passed in the aftermath of the Sandy Hook Elementary School shooting, clarified the statutory authority for federal law enforcement agencies, including those in the Departments of Justice and Homeland Security, to assist state law enforcement agencies, and mandated across federal agencies a definition of "mass killing" as three or more killings during an incident.A mass murder may be further classified as a mass shooting or a mass stabbing. Mass murderers differ from spree killers, who kill at two or more locations with almost no time break between murders and are not defined by the number of victims, and serial killers, who kill people over long periods of time.

A border wall has been 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".

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 agents to suspected migrant crossings. In May 2011, the Department of Homeland Security (DHS) said it had 649 miles (1,044 km) of barriers in place. A total of 438 miles (705 km) of new primary barriers were built during Donald Trump's first presidency, dubbed the "Trump wall", though Trump had repeatedly promised a "giant wall" spanning the entire border and that Mexico would "pay for the wall," neither of which were done. The national border's length is 1,954 miles (3,145 km), of which 1,255 miles (2,020 km) is the Rio Grande and 699 miles (1,125 km) is on land.

The President's Daily Brief, sometimes referred to as the President's Daily Briefing or the President's Daily Bulletin, is a top-secret document produced and given each morning to the president of the United States; it is also distributed to a small number of top-level US officials who are approved by the president. It includes highly classified intelligence analysis, information about covert operations, and reports from the most sensitive US sources or those shared by allied intelligence agencies. At the discretion of the president, the PDB may also be provided to the president-elect of the United States, between election day and inauguration, and to former presidents on request.

The PDB is produced by the director of national intelligence, and involves fusing intelligence from the Central Intelligence Agency, the Defense Intelligence Agency, the National Security Agency (NSA), the Federal Bureau of Investigation (FBI), the Defense Department, Homeland Security and other members of the U.S. Intelligence Community.

The United States Immigration and Customs Enforcement (ICE; pronounced "ice") is a federal law enforcement agency under the supervision of the United States Department of Homeland Security. Its stated mission is to conduct criminal investigations, enforce immigration laws, preserve national security, and protect public safety. ICE was created as part of the Homeland Security Act of 2002 following the September 11 attacks. It absorbed the prior functions of the Immigration and Naturalization Service and the United States Customs Service.

ICE has been involved in multiple controversies throughout its existence, with significant increases in criticism during the first and especially the second administration of Donald Trump. Following the passage of the One Big Beautiful Bill Act in 2025 as part of Trump's hardline immigration policy, ICE became the largest and most well-funded federal law enforcement agency in U.S. history. Its aggressive and anonymized enforcement actions, controversial publicity campaigns, and militarization resulted in significant drops in public support and raised concerns over legality, lack of accountability, and civil rights violations. ICE agents are noted for wearing masks, civilian clothing, and using unmarked vehicles to protect their identity. The agency has been the subject of widespread protests particularly in 2018 and 2025, with some activists calling for its abolition. Since its expansion, the agency has been described by critics, as well as the American Civil Liberties Union, as a growing paramilitary force under Trump's personal control.

The federal government of the United States empowers a wide range of federal law enforcement agencies (informally known as the "Feds") to maintain law and public order related to matters affecting the country as a whole.

While the majority of federal law enforcement employees work for the Department of Justice and Homeland Security, there are dozens of other federal law enforcement agencies under the other executive departments, as well as under the legislative and judicial branches of the federal government.

George W. Bush's tenure as the 43rd president of the United States began with his first inauguration on January 20, 2001, and ended on January 20, 2009. Bush, a Republican from Texas, took office after defeating the Democratic incumbent vice president Al Gore in the 2000 presidential election. Four years later, he won re-election in the 2004 presidential election, after defeating the Democratic nominee John Kerry. Alongside Bush's presidency, the Republican Party also held their majorities in the House of Representatives and the Senate during the 108th and 109th U.S. Congresses following the 2002 and 2004 elections, thereby attained an overall federal government trifecta. Bush was constitutionally limited to two terms and was succeeded by Democrat Barack Obama, who won the 2008 presidential election against Bush's preferred succcessor, John McCain. He is the eldest son of the 41st president, George H. W. Bush.

A decisive event reshaping Bush's administration were the terrorist attacks on September 11, 2001. In its aftermath, Congress created the Department of Homeland Security and Bush declared a global war on terrorism. He ordered an invasion of Afghanistan in an effort to overthrow the Taliban, destroy al-Qaeda, and capture Osama bin Laden. He also signed the controversial Patriot Act in order to authorize surveillance of suspected terrorists. In 2003, Bush ordered an invasion of Iraq, alleging that the Saddam Hussein regime possessed weapons of mass destruction. Intense criticism came when neither WMD stockpiles nor evidence of an operational relationship with al-Qaeda were found. Before 9/11, Bush had pushed through a $1.3 trillion tax cut program and the No Child Left Behind Act, a major education bill. He also pushed for socially conservative efforts, such as the Partial-Birth Abortion Ban Act and faith-based welfare initiatives. Also in 2003, he signed the Medicare Prescription Drug, Improvement, and Modernization Act, which created Medicare Part D.

United States Customs and Border Protection (CBP) is the largest federal law enforcement agency of the United States Department of Homeland Security. It is the country's primary border control organization, charged with regulating and facilitating international trade, collecting import duties, as well as enforcing U.S. regulations, including trade, customs, and immigration. CBP is one of the largest law enforcement agencies in the United States. It has a workforce of more than 45,600 federal agents and officers. It is headquartered in Washington, D.C.

The Transportation Security Administration (TSA) is an agency of the United States Department of Homeland Security (DHS) that has authority over the security of transportation systems within and connecting to the United States. It was created as a response to the September 11 attacks to improve airport security procedures and consolidate air travel security under a combined federal law enforcement and regulatory agency.

The TSA develops key policies to protect the U.S. transportation system, including highways, railroads, bus networks, mass transit systems, ports, pipelines, and intermodal freight facilities. It fulfills this mission in conjunction with other federal, state, local and foreign government partners. However, the TSA's primary mission is airport security and the prevention of aircraft hijacking. It is responsible for screening passengers and baggage at more than 450 U.S. airports, employing screening officers, explosives detection dog handlers, and bomb technicians in airports, and armed Federal Air Marshals and Federal Flight Deck Officers on aircraft.

The United States Secret Service (USSS or Secret Service) is a federal law enforcement agency under the Department of Homeland Security tasked with conducting criminal investigations and providing protection to American political leaders, their families, and visiting heads of state or government. The Secret Service was, until 2003, part of the Department of the Treasury, due to their initial mandate of combating counterfeiting of U.S. currency. The agency has protected U.S. presidents and presidential candidates since 1901.

The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Executive Orders on April 1, 1979. The agency's primary purpose is to coordinate the response to a disaster that has occurred in the United States and that overwhelms the resources of local and state authorities. The governor of the state in which the disaster occurs must declare a state of emergency and formally request from the president that FEMA and the federal government respond to the disaster. The only exception to the state's gubernatorial declaration requirement occurs when an emergency or disaster takes place on federal property or to a federal asset—for example, the 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, or the Space Shuttle Columbia in the 2003 return-flight disaster.

While on-the-ground support of disaster recovery efforts is a major part of FEMA's charter, the agency provides state and local governments with experts in specialized fields, funding for rebuilding efforts, and relief funds for infrastructure development by directing individuals to access low-interest loans, in conjunction with the Small Business Administration. In addition to this, FEMA provides funds for response personnel training throughout the United States and funds for non-federal entities to provide housing and services for migrants released from Department of Homeland Security custody.

The Corps of Cadets at the United States Military Academy (USMA), at West Point, New York, is organized into a brigade. The senior ranking cadet, the brigade commander, is known traditionally as the first captain, a leadership position created in 1872. The first captain is responsible for the overall performance of the 4,400-strong Corps of Cadets, including the implementing of a class agenda and acting as a liaison between the corps and the administration.

The rigid screening process begins with the applications for enrollment being submitted to either Federal-level legislators, or to the president or vice president of the United States. Once enrolled at the academy, each student's performance is closely tracked through the first three years, at the end of which, the individual top-performing cadet is named first captain for the ensuing academic year. Among the notable historical figures who held that position were John J. Pershing, Douglas MacArthur, and William Westmoreland.

The military history of the United States spans over four centuries, dating back to 1607 and pre-dating by nearly two centuries the founding of the nation following the American Revolutionary War. During this moment, the United States evolved from a colonial territory to newly formed nation following its independence from the Kingdom of Great Britain (1775–1783) to ultimately becoming a world superpower in the aftermath of World War II and through the present. As of 2024, the United States Armed Forces consists of the Army, Marine Corps, Navy, Air Force and Space Force, all under the command of the Department of Defense, and the Coast Guard, which is controlled by the Department of Homeland Security.

In 1775, the Continental Congress, convening in present-day Independence Hall in Philadelphia, established the Continental Army, the Continental Navy, and the Continental Marines, formally joining and escalating its war for independence in the Revolutionary War. This newly formed military, fighting alongside the Kingdom of France, triumphed over the British in the war, leading to its independence following the signing of the Treaty of Paris in 1783. In 1789, the new Constitution made the U.S. president the commander-in-chief, and gave Congress the authority to declare war. Major conflicts involving the U.S. military include the American Revolutionary War, American Indian Wars, War of 1812, Mexican–American War, American Civil War, Spanish–American War, World War I, World War II, Korean War, Vietnam War, Gulf War, War in Afghanistan, Iraq War, and the war against the Islamic State.

An active shooter is the perpetrator of an ongoing mass shooting. The term is primarily used to characterize shooters who are targeting victims indiscriminately and at a large scale, who oftentimes, will either commit suicide or intend to be killed by police. More generally, an active perpetrator of a mass murder may be referred to as an active killer.

The Federal Bureau of Investigation defines an active shooter as "one or more individuals actively engaged in killing or attempting to kill people in a populated area", excluding gun-related incidents that were the result of self-defense, gang or drug violence, residential or domestic disputes, crossfire as a byproduct of another ongoing criminal act, controlled barricade or hostage situations, or actions that appeared not to have put other people in peril. In 2008, the United States Department of Homeland Security defined an active shooter as "an individual actively engaged in killing or attempting to kill people in a confined and populated area; in most cases, active shooters use firearms and there is no pattern or method to their selection of victims."

Executive Order 13769, titled Protecting the Nation from Foreign Terrorist Entry into the United States, labeled the "Muslim ban" by President Donald Trump and his supporters and critics alike, and commonly known as such, or commonly referred to as the Muslim travel ban, Trump travel ban, the Trump Muslim travel ban, or the Trump Muslim Immigration Ban, was an executive order signed by President Trump. Except for the extent to which it was blocked by various courts, it was in effect from January 27, 2017, until March 6, 2017, when it was superseded by Executive Order 13780, a second order sharing the same title.

Part of a series of executive actions, Executive Order 13769 lowered the number of refugees to be admitted into the United States in 2017 to 50,000, suspended the U.S. Refugee Admissions Program (USRAP) for 120 days, suspended the entry of Syrian refugees indefinitely, directed some cabinet secretaries to suspend entry of those whose countries do not meet adjudication standards under U.S. immigration law for 90 days, and included exceptions on a case-by-case basis. The Department of Homeland Security (DHS) listed these countries as Iran, Libya, Somalia, Sudan, Syria, and Yemen. Iraq was also included until it was dropped following sharp criticism from the Iraqi government and promises of improved vetting of Iraqi citizens in collaboration with the Iraqi government. More than 700 travelers were detained, and up to 60,000 visas were "provisionally revoked".

Plum Island Animal Disease Center (PIADC) is a United States federal research facility dedicated to the study of foreign animal diseases of livestock. It is a national laboratory of the Department of Homeland Security (DHS) Directorate for Science and Technology (S&T), and operates as a partnership with the U.S. Department of Agriculture (USDA). The facility's director is Larry Barrett.

Isolated on Plum Island off the eastern tip of Long Island, New York, the center has been tasked with protecting America's livestock from animal diseases since 1954. It is the only facility in the country authorized to work with live foot-and-mouth disease (FMD) samples, and specializes in the study of FMD and African swine fever. At the height of the Cold War, study of biological weapons for use against livestock was conducted at the site, ending in 1969 when President Nixon declared an end to the United States' offensive bioweapons program. Today the facility maintains laboratories up to biosafety level 3, and has remained controversial as a result of its high-risk work and proximity to the New York metropolitan area.

Parole, in the immigration laws of the United States, generally refers to official permission to enter and remain temporarily in the United States, under the supervision of the U.S. Department of Homeland Security (DHS), without formal admission, and while remaining an applicant for admission.

Parole has been used since 1956 by presidents of both parties to respond to humanitarian and refugee crises.