All residents and non-resident foreigners with financial affairs in Spain must apply for a NIE number. This number acts as a means of identification and also enables records to be kept of any financial dealings you might have in Spain. Without it you cannot work, open a bank account or buy property. In fact you will be asked for this number in all your official dealings in Spain.
You can apply for your NIE at any national police station with a foreigners’ department where you will need to complete a short form. Many people pay a lawyer or gestor (legal administrator) to apply on their behalf, as a basic knowledge of Spanish is generally needed to communicate with staff and to complete the form.
If you choose to apply yourself it is best to arrive at the police station early to avoid lengthy queues. You will need to take your passport plus a photocopy.
Your NIE can be collected from the police station after a wait of between one week and three months. If you have a work contract or a letter from a Spanish employer or business stating the need for you to have a NIE, you can expect to receive it sooner rather than later.