This process should be simple enough. It serves several purposes:
1) it gives the local council an idea how many people live in its district
2) you get the nearest doctor assigned
3) you get a social security number assigned, once you start working
To register all you need is your passport or DNI and proof of address. Hehe, easier said than done! how many of you live in a flat with 4 others and have nothing in your name? how many of you live in a flat and don't even know whose name is on the tenancy agreement. And if you know the name, do you know the person? Not to panic. There are ways.
The easiest is the tenancy agreement, a water, gas, electricity or phone bill. No mobile phone bill allowed. Telephonica is always appreciated and in theory Menta(Auna) should work too, but you'd be suprised at the confusion such a document can cause. if you plan on using a menta bill, make sure you don't budge and persist on the fact that it is a land line, not a mobile and that it is valid according to their own rules.
Should you not have any such document but know the person whose name is on the tenancy agreement you can ask for a form which they have to fill in and sign and you can go together with that form and a copy of the tenancy agreement to register. Better if the person in question comes with you with his passport, just to be on the safe side.
You are supposed to sign up at your local town hall, but if you're not sure where that is then you can visit the main building in charge of Ciutad Vella and sign up there too. to be found on C/ Ramellers 13 facing the square where Kasparo is situated.
If your leaving the country you also need to un-enroll from your 'empadronamiento'
You must let the local council know in a letter that you would like to unsubscribe you empadronamiento – ‘baja de patron’ – this letter can go to any citizen ‘Oficina de Atención’. You must include in the letter your personal details, address of you empadronamiento and attach a photocopy of an identity document (passport).
All the addresses where you must send this letter to are at http://www.bcn.cat under ‘Directorios’, "OAC" in "Nombre Entidad".