In Canada, a nine digit number issued by the government that is required to work in Canada, as it is used to track earnings & RRSP/RRIF/RESP contributions for tax purposes. The first digit indicates the Province where the number was issued (for example, British Columbia SIN numbers start with a 7, while numbers issued to non-residents start with a 9), the next seven digits are random, and the last digit is kind of checksum used to identify falsified SIN numbers. Most people have a creditcard sized card with their SIN number embossed on it along with their full name which is issued at the same time the number is, but the card is not required to use the SIN number. While most provinces have a minimum age for workers in most industries, SIN numbers are issued at any age - they are useful for instance for parents setting up a Registered Education Savings Plan for their young children - for the plan to be registered in the child's name, they need a SIN.