The Immigration and Naturalization Service (INS) issues green cards --identity cards technically known as Alien Registration Cards -- to citizens of foreign countries who are permanent residents in the United States. Permanent residents have all the rights and privileges of U.S. citizens, except that they cannot vote, have U.S. passports, or leave the U.S. for more than one year without losing their permanent resident status.
After five years of living in the U.S., permanent residents are eligible to apply for naturalization to become U.S. citizens. After receiving an application, the INS recommends to state and federal courts whether or not it should be approved. If favorable, the courts act on this recommendation and formally grant approval and administer the oath of citizenship to the applicant. At this time, the former alien becomes a U.S. citizen with all the rights guaranteed under the U.S. Constitution.