What is residencia?
All EU and EEA (European Economic Area) citizens and their family members have the right to visit, live or work in Spain. For stays of up to 3 months there is no need to register as a resident, or obtain any Spanish documentation unless the you are going to be working, or for example buying a property, in which case you’ll need an NIE. After that period, the official line is, that in order to have the right to reside for more than 3 months, you are expected to meet certain conditions, e.g. you are student, have employment or other means to support oneself.
Someone coming to live or work in Spain long term would typically apply for a residency card, (Tarjeta de Residencia), which confirms an individuals residency status in Spain.
The process for obtaining residencia is similar to that for getting an NIE. The National Police, (Cuerpo Nacional de Policia), control it’s issue. The main difference is that as part of the application, you have to prove that you meet the conditions to be granted the right to reside permanently in Spain. In most cases this will mean demonstrating that you have employment and paying Social Security, or otherwise have means to support yourself financially and have other cover or means of access to healthcare.
Originally the tarjeta de residencia was a robust laminated plastic card (the size of a credit card) with a photograph of the holder of the card and a fingerprint. This was scrapped and replaced with an A4 sized paper certificate, which has been superseded by the current certificado de residencia, which is credit card sized, however made from paper rather than plastic.
The residencia card doesn’t have an expiry date on it. It includes name, NIE, date of birth, place of birth, nationality and your address in Spain, and is only valid accompanied with national photographic ID, such as passport.