NIE and TIE are the two terms that confuse almost every foreigner in Spain — and mixing them up causes real problems. A NIE is simply a tax identification number; it lets you buy a property, open a bank
account or pay taxes, but it does not, on its own, give you the right to
live in Spain.
A TIE is the physical residency card that non-EU nationals need if they are staying longer than the standard tourist period.
Add different visa categories, an appointment system that books up
months in advance, and local council registration (empadronamiento) that most newcomers don’t realise they even need, and it’s easy to end up out of compliance without knowing it.