The NIE is your all-purpose identification and tax number in Spain. You need it for everything that involves a tramite or official process in Spain. For example, you will need an NIE number to buy a property, buy a car, get connected to the utilities and, most importantly as far as the Spanish state is concerned, pay your taxes. Without an NIE number, the Spanish tax authorities are unable to assess or process annual tax payments such as income tax (IRPF), and the annual wealth tax (Patrimonio), both of which are declared by resident and non-resident property owners.
