"Since the September 11 terrorist attacks, considerable concern has been raised because the 19 terrorists were aliens who apparently entered the United States legally despite provisions in immigration laws that bar the admission of terrorists. Fears that lax enforcement of immigration laws regulating the admission of foreign nationals into the United States may continue to make the United States vulnerable to further terrorist attacks have led many to call for revisions in the policy and possibly changes in who administers immigration law. Foreign nationals not already legally residing in the United States who wish to come to the United States generally must obtain a visa to be admitted, with certain exceptions noted in law. Under current law, two departments -- the Department of State (DOS) and the Department of Justice (DOJ) -- each play key roles in administering the law and policies on the admission of aliens. DOS's Bureau of Consular Affairs is the agency currently responsible for issuing visas, and DOJ's Immigration and Naturalization Service (INS) plays a key role in approving immigrant petitions and in inspecting all people who enter the United States. In FY2000, DOS issued approximately 7.5 million visas and rejected over 2 million aliens seeking visas."
CRS Report for Congress, RL31512