You will need a Social Insurance Number (SIN) when you come to settle in Canada or you come to work for a period of time. SIN is a 9 digit number and you will need it to apply for a job, pay taxes, and get credit or mortgage. You can apply for SIN at any Human Resources Development Centre in Canada or download and print the application online at http://www.hrsdc.gc.ca/en/cs/sin/0300/0300_000.shtml.
SIN application forms are available at any post office as well.

Accompanying the application you will need some documents proving your identity. All documents must be originals. You will need your passport or birth certificate, your visa or PR card, and supporting documents showing your name and date of birth. For example if your surname has changed by marriage, you must submit a marriage certificate. To apply for a SIN you have to be a Canadian Citizen, Permanent Resident or Temporary Resident.

It usually takes about 2 weeks to get your SIN card in the mail or you can go and pick it up from your nearest HRSDC branch.

Keep your SIN in a safe place!