What is an RFC? stands for “Registro Federal de Contribuyentes” (Federal Taxpayers Registry) and it is Mexico’s federal tax identification number. An RFC number identifies a taxpayer and so it is the number under which taxes are filed. All Mexicans must have an RFC number. Foreigners and Nationals are allowed to use a generic RFC number by a notary public when buying real estate in Mexico. To exempt when selling a generic RFC is of no use.