A NIE Number is a tax identification number used in Spain. Prior to purchasing a property, selling a property, obtaining a mortgage, starting up a business or working in Spain, it is a requirement by law that every individual possesses an NIE Number. The NIE Number is issued by the Spanish National Police and is printed out on a piece of paper; this is then also often used as a form of identity. A NIE card the size of a credit card is also given to you. Once you have been issued an NIE number, it is yours for life. If you are in the UK and cannot visit Spain to obtain your NIE number in person, it is likely that you may need the help of a UK Notary to obtain one.
