Some people who come to Spain are afraid of getting a NIE (the Spanish foreigners’ identity number) because they think that they may be taxed by the Spanish Government. This identity number is necessary for every foreigner living in Spain; having this does not mean you have to declare taxes.
It is not necessary to have a NIE to rent a property, with a passport alone is sufficient. However, you will need a NIE for opening a bank account, having a business, signing a contract, purchasing a property or a car and for some other transactions.
Lawyers can help you get a NIE but if you do not wish to ask yours, you can personally apply for it by scheduling an appointment at the local police station, with your valid passport and the official application form.
Applying for a NIE is an easy process, you can go online on the Ministry of Foreign Affairs of Spain website and download the application form EX-15; it is important to fill this form up in Spanish language and not in any other language.
This identification number does not change, and it is a lifetime.
Having a NIE does not mean you live in Spain; if you are going to live in Spain you need to have a residency permit. Also, to be able to work in Spain you will need a residency and work permit. If the person is an EU citizen, they can obtain it at the police station at the passport’s office. And non-EU citizens they must apply for it and obtain it at the Consulate or Embassy of their home country.