Question: where do i find my national identification number

title: National identification number
text: In the United States , a Selective Service Number must be applied for by all male citizens turning age 18 . An optional national identity number is the Social Security number ( SSN ) , a nine - digit number issued to U.S. citizens , permanent residents , and temporary ( working ) residents . Its purpose was to identify individuals for the purposes of Social Security , but it is now also used to track individuals for taxation purposes . There is no legal requirement to have a SSN if it is not required for Social Security or taxation purposes , but in practice one is required for many other purposes , for example to open a bank account or apply for a driving license , so that nearly all U.S. citizens and permanent residents have one . The SSN has therefore become a de facto national identification number , despite the fact that originally it was expressly not for this purpose , and in fact a valid SSN can be easily guessed , as they are issued serially 

Answer: answer: There is no legal requirement to have a Social Security number if it is not required for Social Security or taxation purposes, however, the SSN has become a de facto national identification number in the United States.
answer: The Social Security number has therefore become a de facto national identification number.