The United States Customs and Immigration Services (USCIS) is the government agency that oversees lawful immigration to the United States. The agency has 19,000 government employees and contractors working at more than 200 offices across the world.
This is the mission statement for USCIS:
U.S. Citizenship and Immigration Services administers the nation’s lawful immigration system, safeguarding its integrity and promise by efficiently and fairly adjudicating requests for immigration benefits while protecting Americans, securing the homeland, and honoring our values.