Every American-born child is issued a social security number and social security card upon his or her birth. This is a way for Americans to identify themselves as citizens and prove their eligibility to work in the country. Foreigners may apply for numbers and cards, so that they can get the permission to work in the United States. Each number is unique and consists of the "area" (a 3-digit number assigned according to the area code in which the application for a social security number is sent), the group and a serial number, which runs consecutively from 0001 to 9999.