Social Insurance Number

A social insurance number (SIN) is a number issued in Canada to administer various government programs. The SIN was created in 1964 to serve as a client account number in the administration of the Canada Pension Plan and Canada's varied employment insurance programs. In 1967, Revenue Canada (now the Canada Revenue Agency) started using the SIN for tax reporting purposes. SINs are issued by Human Resources and Skills Development Canada (previously Human Resources Development Canada).

The SIN is formatted as three groups of three digits (e.g., 123-456-789).

The top of the card has changed over the years as the departments that are responsible for the card have changed:

The 2012 Canadian federal budget contained provisions to phase out the Social Insurance Number cards because they lacked modern security features and could be used for identity theft. As of 31 March 2014, Service Canada no longer issues plastic SIN cards. Instead, an individual will receive a paper "Confirmation of SIN letter".

Through functionality creep, the SIN has become a national identification number, in much the same way that the Social Security Number has in the United States. However, unlike in the US, in Canada there are specific legislated purposes for which a SIN can be requested. It is not an identity document.

Unless an organization can demonstrate that the reason it is requesting an individual's SIN is specifically permitted by law, or that no alternative identifiers would suffice to complete the transaction, it cannot deny or refuse a product or service on the grounds of a refusal to provide a SIN. Examples of organizations that legitimately require a SIN include employers, financial institutions that provide interest on deposits, and federal government agencies. Giving a SIN when applying for consumer credit, such as buying a car or electronics, or allowing it to be used as a general purpose identification number, such as by a cable company, is strongly discouraged.

...
Wikipedia