An NIE number is a Spanish tax identification number and you will need one if you are both a resident or non-resident foreigner from any country that carries out transactions in Spain.
What an NIE number is and where it is required
It is a Spanish tax identification number that the Spanish authorities assign to any foreigner. It is essential when making any fiscal transaction that require you to pay taxes to the Spanish Inland Revenue Office. It appears and will be required in all Spanish documents and does not expire so it will always be of use to you when being a part of transactions in Spain.
Why you would need an NIE number
It is a legal requirement (whether you are within or outside of the EU) that is needed for tax purposes. If you are buying and selling property in Spain then an NIE number is required but it is also needed for even more things such as being paid for employment and even if you are even applying for a Spanish drivers licence which will likely be essential for residents.
How Lawindexpro can help
Using our contacts we can submit documents that our Spanish Solicitor will prepare for you to the relevant authorities in Spain.