Foreigner Identity Number (NIE)
Foreigners who, for their economic, professional or social interests, are related to Spain, will be endowed, for identification purposes, with a personal number, unique and exclusive, of a sequential nature.

The personal number will be the foreigner's identifier, which must appear on all documents that are issued or processed, as well as the procedures that are stamped on your identity card or passport.

For the assignment of NIE due to economic, professional or social interests, the following requests will be accepted:

Those presented in Spain personally by the interested party,
Those presented in Spain through a representative,
Those that appear in the Diplomatic Representations or Spanish Consular Offices located in the country of residence of the applicant, corresponding to their demarcation of residence.
For the allocation of said number, the following documents must be provided:

Standardized application-form (EX-15), duly completed and signed by the foreigner.
Original and copy of the full passport, or identity document, or travel title or registration card in force.
Communication of the economic, professional or social causes that justify the request.
When requested through a representative, he shall prove that he has sufficient power stating expressly that he is empowered to make such a request.
Note on the validity of foreign public documents: To check the necessary requirements regarding the legalization and translation of foreign public documents, you can consult the information sheet of the General Secretariat for Immigration and Emigration (see in EXTERNAL LINKS).

EXTERNAL LINKS
Information sheet on legalization and translation of documents of the General Secretariat for Immigration and Emigration
Electronic headquarters of the General Police Directorate (immigration procedures)
 

What is the NIE for?

It is vitally important for residents and property owners in Spain - The NIE is required for foreigners (including EU citizens) who intend to live or own a property in Spain. In essence, the NIE is necessary for any economic activity in Spain (even if the NIE holder is taxed in another jurisdiction), such as buying or selling property, registering with the tax office and paying taxes in general , buying or selling a vehicle, obtaining a driver's license, owning a business, working, accessing social security and health services, public services (for example, contracting water and electricity), opening a local bank account (although not necessary for a “non-resident” bank account), accepting an inheritance, etc.

Very important :

The NIE is not a visa or residence permit - The NIE does not grant a visa or a residence permit per se. However, for the foregoing, it is one of the requirements for foreigners who wish to reside in Spain.
This does not imply tax residence - Although the NIE certificate may indicate that the owner is a resident of Spain. In reality, this does not imply or provoke tax residency per se. The concept is tax residence (or tax domicile) is different. At the time of this article, an individual becomes a tax resident in Spain for residing 183 or more days a year in Spain (that is, more than half of the year cumulatively).

This does not imply local residence - Foreigners who own the property or who live in Spain must register in the “municipal register” (that is, the municipal lists of inhabitants in a local community). Related to the NIE, registration in the register also does not imply fiscal residence. However, registration is recommended to ensure: (I) the reduction of taxes with respect to IBI (depending on the policy of the local council); (II) access local services; and (III) greater central government investment in local services and infrastructure.