U.S. Immigration and Customs Enforcement ( ICE ) is the largest and primary law enforcement agency of the United States Department of Homeland Security ( DHS ) . U.S. Immigration and Customs Enforcement ( ICE ) is a federal law enforcement agency under the United States Department of Homeland Security ( DHS ) , responsible for identifying , investigating , and dismantling vulnerabilities regarding the nation 's border , economic , transportation , and infrastructure security . The largest components within DHS are Homeland Security Investigations ( HSI ) and Enforcement & Removal Operations ( ERO ) .