The required documents are:
- Valid passport.
- Proof of the reason for the application (purchase contract, deed, inheritance certificate, employment contract, etc.).
- Form EX-15 (the official application).
- Fee 790 code 012 paid.
If you apply for the NIE through a representative, you also need a specific power of attorney. If that power of attorney is signed outside Spain, it must bear a Hague Apostille or consular legalisation depending on the country.