For citizens who are going to stay in Spain for less than three months. (Do not confuse with the EU Certificate, which is a different procedure, mandatory for EU citizens who will stay in Spain for more than 3 months).
You can obtain more information at this link: Immigration Offices Information DOCUMENTS TO SUBMIT: Application completed on the free official form EX-15 (pdf), original and copy, specifying the reason for needing an NIE number. Proof of the appointment.
A printout or a screenshot from the mobile phone will be accepted. Valid passport or original identity document of your country of origin (the latter only for citizens of EU countries).
Proof of entry into Spain if you entered Schengen territory through another country. If the application is made by power of attorney, a notarial power of attorney, legalised and translated if the notary who issued it is not in Spain, and a legalised copy of the complete passport will be provided.
Fee model 790 (code 012) of the Directorate-General of the Police, paid at any bank. The form must be downloaded directly from the internet at the following link: https://sede.policia.gob.es:38089/Tasa790_012 The fee must indicate "Assignment of NIE number".
The fee payment document CANNOT be photocopied. READ CAREFULLY Only one person will be attended per appointment requested (Mandatory).
The document will be delivered to the interested party or authorised person from the fifth working day after its request. An original and a copy of all documentation must be provided.
All documentation must be submitted in Spanish. NOTE: For cases exclusively of EU Citizens who do not have a passport but do have an identity document, they may enter the number of that document in the PASSPORT field.