The Padron — registering at your town hall
The Padrón Municipal de Habitantes is the local register of residents. You need it for almost everything: applying for public healthcare, registering children in school, renewing your driving licence, or proving how long you've lived in Spain. It's free and mandatory if you live in Spain more than 6 months a year.
You register at the town hall (ayuntamiento) of your municipality. Lanzarote has seven municipalities — Arrecife, Teguise, Tías, San Bartolomé, Yaiza, Tinajo and Haría — and each one handles its own. The process is straightforward: you fill in a form, show your passport/NIE and proof of address (rental contract, utility bill, or deed if you own), and they issue a certificado de empadronamiento. Renewal is required every 2 years for non-EU citizens and every 5 years for EU citizens and Spaniards.