NIE is the Numero de identidad de extranjero, the identification number of a foreigner. It is required for financial and legal procedures, like buying a property, tax payments, applying for documents when moving to the country and etc. NIE is issued by the Spanish Immigration Office. To apply for the NIE, you need to stay legally in the country for a certain period of time (for example, studying or holidays) and have compelling reasons for its obtaining (buying a property and etc).
