USCIS is part of the U.S. Department of Justice. The enforcement of immigration law is vested in the Attorney General, but the Attorney General usually delegates authority to the USCIS.

USCIS is part of the U.S. Department of Justice. The enforcement of immigration law is under the authority of the Attorney General, but the Attorney General usually delegates authority to the INS, so the INS has become the central enforcement agency for immigration law, specializing in immigration and non-immigrant applications, entry and exit of foreign nationals, border patrols, arrest and deportation of illegal aliens, refugee screening, punishment for illegal employment, and more. The four Regional Immigration Service Centers (Regiona l Service Center), which handle immigrant and non-immigrant applications, and the District Office and Suboffice, which handle day-to-day immigration matters, are the ones that foreigners deal with the most. The latter is commonly known as "Local Immigration Bureau" (Local Office).

Thus, the Bureau of Immigration has become the core enforcement agency of immigration law, specializing in the processing of immigrant and non-immigrant applications, the entry and exit of foreign nationals, border patrols, the arrest and deportation of illegal aliens, refugee screening, penalties for illegal employment, and more.

The most common foreigners deal with the four Regional Immigration Service Centers (Regiona l Service Center), which directly handle immigrant and non-immigrant applications, and the immigration sub-offices (District Office) and offices (Suboffice), which handle day-to-day immigration matters. (Suboffice). The latter is commonly known as the "Local Immigration Office" (Local Office).