Until 2003 most immigration functions sat in one agency, the Immigration and Naturalization Service at the Justice Department. The Homeland Security Act split those functions among three new agencies and left immigration courts at Justice. The result is a system in which a single case may pass through four or more agencies.
This guide explains which agency does what, how a case moves through the system, and the debates over immigration enforcement.
Removal cases are heard by immigration judges in the Justice Department's Executive Office for Immigration Review, not by the federal judiciary. Appeals go to the Board of Immigration Appeals and then to the federal courts of appeals, and the Attorney General can overrule board decisions. The courts face a backlog of millions of cases, and there is no right to a government-appointed lawyer. In 2025 the administration dismissed many immigration judges and added temporary judges, while expanding expedited removal, which bypasses the courts.
The Constitution gives Congress power over naturalization, and the Supreme Court has recognized broad federal power over immigration. For most of the twentieth century, the Immigration and Naturalization Service handled both benefits and enforcement. After the September 11 attacks, Congress abolished it and split its duties among U.S. Citizenship and Immigration Services, Customs and Border Protection, and Immigration and Customs Enforcement, all in the new Homeland Security Department, beginning in 2003.
Supporters of the expanded enforcement say it restores control of the border, upholds the law, and protects American workers and communities. Critics say it has separated families, detained people with no criminal records, strained due process, and harmed industries that rely on immigrant labor. Broader debates include legal immigration levels, asylum rules, the status of long-term residents and those brought as children, and whether the fragmented agency structure should be reorganized. Congress has not passed comprehensive immigration reform since 1986.
USCIS decides applications for family and employment green cards, naturalization, work permits, asylum claims filed affirmatively, refugee admissions abroad, and humanitarian programs such as Temporary Protected Status. It is funded mainly by application fees and conducts the civics and English tests for citizenship. The State Department's Bureau of Consular Affairs issues visas at embassies and consulates, and the Labor Department certifies that some employment-based immigrants and temporary workers will not harm American workers.
Customs and Border Protection inspects travelers and cargo at more than 300 ports of entry through its Office of Field Operations, while the Border Patrol polices the land borders between ports. Encounters at the southwest border reached record highs in 2022 and 2023 and then fell sharply in 2024 and 2025 after new restrictions and enforcement, reaching their lowest levels in decades. Unaccompanied children apprehended at the border are transferred to the Department of Health and Human Services for care.
ICE's Enforcement and Removal Operations arrests, detains, and deports noncitizens, while Homeland Security Investigations pursues smuggling, trafficking, and other crimes. Since 2025 the administration has expanded arrests, worksite operations, and detention, aided by a 2025 budget law that provided tens of billions of dollars for detention and hiring, and it has used other agencies and the National Guard to assist. Detention reached record levels, and many tactics and policies, including use of the Alien Enemies Act of 1798, were challenged in court.
See the department that houses most of these agencies in the homeland security agencies, compare other federal police in federal law enforcement agencies, or learn about naturalization in the U.S. civics test explained.