Before 2003, the functions now in Homeland Security were scattered across the Justice, Treasury, Transportation, Agriculture, and other departments. The 9/11 Commission and Congress concluded that poor coordination had left the country vulnerable, and the Homeland Security Act of 2002 brought them together under one secretary.
This guide explains the department's main components, what each does, and the debates over its structure and priorities.
Supporters of the department say unified leadership improved coordination and information sharing after 9/11. Critics argue that it combines too many unrelated missions, that immigration enforcement crowds out disaster response and cybersecurity, and that agencies such as FEMA or the Secret Service would work better on their own. The expansion of immigration enforcement since 2025 has drawn praise from those who see it as restoring border control and criticism from those concerned about civil liberties, detention conditions, and due process.
The Homeland Security Act, signed November 25, 2002, created the department, which began operating in March 2003. It absorbed the Customs Service from Treasury, the Immigration and Naturalization Service from Justice, the Coast Guard and the new Transportation Security Administration from Transportation, FEMA, the Secret Service, and others. The merger was difficult, and the department long ranked near the bottom of federal surveys on employee morale. Congressional oversight remains split among more than 100 committees and subcommittees.
The Federal Emergency Management Agency coordinates federal disaster assistance after the President declares a disaster, funding rebuilding, individual aid, and preparedness grants. The Cybersecurity and Infrastructure Security Agency, created in 2018, helps protect federal networks, critical infrastructure, and election systems. In 2025 both agencies lost staff, and in May 2026 a presidentially appointed FEMA Review Council recommended a smaller FEMA that would shift more disaster responsibility to states, with fewer federal declarations. Supporters said states are better positioned to manage most disasters, while critics warned that poorer states could be left without help.
The Transportation Security Administration, created after 9/11, screens about 2.5 million or more air passengers on busy days and sets security rules for airports, pipelines, and transit. The Coast Guard, a military service, conducts search and rescue, maritime law enforcement, drug interdiction, and port security. The Federal Law Enforcement Training Centers train officers for most federal agencies.
The Secret Service protects the President, the Vice President, major candidates, and visiting leaders, and investigates financial crimes. After the July 2024 assassination attempt on a presidential candidate in Pennsylvania, independent reviews found serious security failures, leading to leadership changes and reforms. The Office of Intelligence and Analysis shares threat information with state and local partners, and the Science and Technology Directorate supports research. The department's secretary sits on the National Security Council.
Customs and Border Protection, the largest federal law enforcement agency, inspects travelers and cargo at ports of entry and patrols between them through the Border Patrol. Immigration and Customs Enforcement detains and removes noncitizens and, through Homeland Security Investigations, pursues smuggling, trafficking, and other crimes. U.S. Citizenship and Immigration Services processes visas, green cards, asylum claims, and naturalization. A 2025 budget law provided large funding increases for detention, hiring, and border infrastructure.
See the immigration side in detail in who handles immigration, compare other federal police in federal law enforcement agencies, or see the intelligence agencies in the intelligence community.