Department of Homeland Security (DHS)
DHS is comprised of three main organizations responsible for immigration policies, procedures, implementation and enforcement of U.S. laws, and more. These DHS organizations include United States Citizenship and Immigration Services (USCIS), Customs and Border Protection (CBP) and Immigration and Customs Enforcement (ICE). Together they provide the basic governmental framework for regulating the flow of visitors, workers and immigrants to the United States. USCIS is responsible for the approval of all immigrant and nonimmigrant petitions, the authorization of permission to work in the U.S., the issuance of extensions of stay, change or adjustment of an applicant's status while the applicant is in the U.S, and more. CBP is responsible for admission of all travelers seeking entry into the U.S., and determining the length of authorized stay, if the traveler is admitted. Once in the United States the traveler falls under the jurisdiction of DHS. Visit the DHS Internet site for more information.
Source: U.S. Department of State.