This number is used for taxes, pensions, unemployement and so it is necessary for contracts , to start a business or when becoming self employed. It also gives you access to the public health care system to which every worker is entitled to.
Once someone enters the system and obtains a social security number, this number does not change. In most cases, for members of the EU, and husbands, spouses and family of Spanish citizens, getting a SS number is as easy as presenting a valid ID (NIE or DNI). In some cases you might be required to show an employment contract, specially if you are a non-EU citizen (and sometimes even if you are), so make sure you carry one just in case.
How to obtain your Social Security number.
- You need to find your nearest Social Security Office, the one nearest to your residence. You can find this information online here. You don’t need an appointment, just to get there (opening hours 9:00-14:00), grab a number and wait for your turn.
Do not go at the start or the end of the month because that is when most people go to solve issues with taxes or pensions. The best option is to be there at 8:30, 8:45 some day from the 5th to the 25th.
You might have problems with the touchscreen and knowing what option to select, just ask there, they will help you.
- The next step is to fill in the form. You can ask for it at the SS office, but it’s better if you carry it with you and fill it in before you go. The form you need (if nothing has changed) is TA.1 which can be downloaded here.
You just need your NIE number, but take with you your passport and employement contract just in case.
It won’t take more than 45 days to get your number, although in most cases it takes much less and they might give you your number on the spot.
More information here (Spanish).