A Social Insurance Number (SIN) is a unique nine-digit number that identifies you to the Canada Revenue Agency (CRA) and other government departments and agencies. It is used to track your income and contributions to government programs such as the Canada Pension Plan and Employment Insurance.
You need a SIN to work in Canada or to access certain government benefits and services. If you are a Canadian citizen, permanent resident, or protected person, you can apply for a SIN online, by mail, or in person at a Service Canada office.