What Are SSN and SIN?

If you dread a future in which countries keep track of their citizens with identification numbers rather than names, it's time to face the truth: that future is already here. The United States assigns citizens unique Social Security numbers (SSN) that keep track of taxes and benefits, and it has done so for years. It is hardly alone. Many governments around the world revert to numbers to keep things organized. For example, the country's neighbor to the north, Canada, does the same thing, but calls them Social Insurance numbers, or SIN.

A Social Security number is issued by the United States government's Social Security Administration to U.S. citizens and legal residents. The numbers are unique, each nine digits. Initially, the first three of the digits were assigned by geographic location, with people on the East Coast getting the lowest numbers and those on the West Coast assigned the highest. However, this system has been phased out in favor of a random assignment.

SSNs were initially issued to keep track of the people participating in the nation's disability/retirement insurance system, Social Security. It is a pay-in system, meaning that it is financed by Social Security taxes imposed on wages. The collected Social Security taxes go into a trust fund that is, in turn, used to make payments to retirees and their spouses and children. However, the government quickly realized how useful it was to have unique identification numbers for all Americans and began using the number to manage taxes and other government programs.

Today, your Social Security number is a core identification that you have to provide to your employer for tax withholding. You also have to use the number when you are filing your tax returns. It serves as valid identification and proof of legal status in the country if you are applying for a passport or a driver's license.

Read More: Who Is Not Eligible for a Social Security Number?

Do you have to get a Social Security number? You must have an SSN if you are employed and receive wages. If you pay income taxes and claim dependents, you need an SSN for each minor child you list as a dependent. You'll also have to get one to participate in the Social Security insurance program.

Most citizens are assigned an SSN at birth, with hospitals expediting the application process for newborns. However, you can apply at any age using the form SS-5. If you are over 12 years old, you will need to go in for an interview and present original documents that prove your identity as well as your citizenship. If you were not born a citizen, you must prove naturalization. Noncitizens with a legal right to work in the country can get an SSN by establishing their identity, immigration status and age. It is also possible for someone not authorized to work in the country to get an SSN to obtain certain government services.

If you are confused about SSN versus SIN, just think geographically. The Social Insurance number is a unique number issued to Canadians by the government of Canada for many of the same reasons the U.S. government issues SSNs. It is also a nine-digit number and is required before individuals can work in Canada or qualify for government benefits and programs. The Canadian government also uses the SIN as a core method of identification.

Like the SSN, an SIN is often issued to a newborn a child via Canada's Newborn Registration Service. However, anyone who is eligible can apply for an SIN and must do so in order to hold a job or receive government benefits. You must apply in person if you are in the country, and provide documentation proving your identity and eligibility,