A Personal Public Service number is your unique reference number for all your dealings with the Public Service (e.g. applying to the tax office for a tax credits certificate, applying to the Department of Social, Community, and Family Affairs for a Social Welfare payment scheme etc)  The PPS number replaces the RSI number (Revenue and Social Insurance Number).  If you already have an RSI number this is now your Personal Public Service number.  More information about the PPS number can be obtained at the Department of Social Welfare website