People from outside the European Union, and one should probably add British citizens to that list now as the UK prepares to leave the EU in March 2019, need Spanish citizenship if they want to reside in Spain on a permanent basis. There are of course quite stringent regulations governing citizenship, but let’s look at what is required.
If you have lived in Spain for five years you can apply for permanent residence. Once you have lived in Spain for ten years you can make an application for Spanish nationality. However, with regard to the latter, the ten-year rule can be reduced if you are married to a Spaniard, or you have a parent who is a Spanish national.
It’s also important to remember that there is a difference between permanent residency and Spanish citizenship. If you hold an EU long-term permanent residence permit you can stay resident in Spain indefinitely, while still keeping your original nationality and passport. Being a Spanish permanent resident gives you the same rights in Spain as a Spanish national, as long as you can support yourself and your family financially, and you must have proof of public or private health insurance. For those applicants who are not originally EU citizens, having permanent residency only allows travel within the EU for limited periods.
On the other hand, if you become a Spanish citizen you will have to give up your original nationality and passport. However (and this is most pertinent to non-EU applications), you will have all the rights of a Spanish national, enjoy freedom of movement throughout the European Union, plus, you will be able to vote in European elections.
Do remember, that only non-EU nationals can apply for an EU long-term residence permit.
The documents you will have to submit are:
• a valid passport
• proof of legal residence in Spain e.g. a long-term rental contract or rent receipts
• criminal record certificate issued by the authorities in your home country
• medical certificate (certificado medico), if the applicant didn’t present it when applying for temporary residence
• proof that healthcare is guaranteed during your residence in Spain
• marriage or divorce certificate or other papers relating to your marital status (translated into Spanish if required)
Also, if you hold an EU long-term residence permit granted by another EU member country and want to stay on in Spain, you will have to give up the long-term residence status in that country and apply for an EU long-term residence permit from the Foreigner’s Office (Oficina de Extranjeros) in Spain.