Tax Identification Number (TIN) is a common international term for what is referred to in the Australian tax system as a Tax File Number (TFN). In the case of U.S. persons or U.S. tax residents, the TIN will be your U.S. Social Security Number (SSN). United Kingdom does not have a ‘TIN’ as such but two numbers which are used as a proxy for TIN for UK tax residents are either National Insurance Number (NINO) or Unique Taxpayer Reference (UTR). For New Zealand, the TIN is the Inland Revenue Department (IRD) number and Canada is the Social Insurance Number (SIN). A list of countries and the relevant TIN format can be found here.