Useful Items Publication 15  Circular E, Employer's Tax Guide 15-A  Employer's Supplemental Tax Guide 51  Circular A, Agricultural Employer's Tax Guide 519  U.S. Tax Guide for Aliens 901  U.S. Tax Treaties Form (and Instructions) SS-4  Application for Employer Identification Number W-2  Wage and Tax Statement W-4  Employee's Withholding Allowance Certificate W-4P  Withholding Certificate for Pension or Annuity Payments 941  Employer's Quarterly Federal Tax Return 1042  Annual Withholding Tax Return for U.S. Source Income of ForeignPersons 1042-S  Foreign Person's U.S. Source Income Subject to Withholding