How can I reside legally in Spain after the end of the transition period on 31 December 2020?

To reside legally in Spain after December 2020 you need to legalise your stay by obtaining the new Foreigner’s Identity card (called TIE or Tarjeta de Identidad de Extranjero), being a holder of an the EU Residency certificate (Certificado UE/Green Card) or by obtaining an EU-Member Family Card. 

This will allow you to benefit from the provisions of the Withdrawal Agreement and continue enjoying your rights in Spain as before. The Foreigner’s Identity Card (TIE), EU Residency Certificates (Green card) and ID cards of family members of the EU citizen obtained before the end of the transition period will subsequently serve to accredit their legal residence in Spain and benefit from the provisions of the Withdrawal Agreement. 

It is important to note that since July 6 2020 British nationals will have to apply for the new TIE document instead of the EU Residency Certificate.