The . Citizenship and Immigration Services (formerly the Immigration and Naturalization Service) and Immigration and Customs Enforcement are components of the Department of Homeland Security and handle the processing, enforcement, and adjudication of . immigration matters. immigration laws treat persons as either citizens or aliens. The law classifies aliens according to immigration status, with each group afforded different rights and obligations, such as the right to reside in the United States, the right to sponsor relatives, and the right to work in the United States. Aliens may be lawful permanent residents (., green card holders), immigrant visa holders, temporary lawful visitors, or undocumented persons.