A BSN (Burgerservicenummer) / Sofi number (social security number) is the citizen service number; a unique registration number for everyone who lives in the Netherlands. A BSN facilitates any interaction with the Dutch authorities; deducting your taxes and social security contributions, registering with the health insurance, opening a bank account, getting paid, being entitled to benefits etc. Put simply, the Burgerservicenummer is the first bureaucratic issue that people who come to live in the Netherlands have to deal with. To apply for a BSN at the City Hall, EU citizens need to provide a valid proof of identity (not a driving license) and their registered address, while for non-EU expats other documents (residence permit, registration, employment contract etc.) have to be presented too. A confirmation of your town hall registration will be sent a couple of weeks later. In case your stay in the Netherlands is not going to be longer than four months, you have to apply for a Sofi number (social-fiscal number). Again, you have to contact your local tax office (Belastingdienst) and arrange an appointment. The procedure as well as the necessary documentation is exactly the same as for the BSN.