To work in the Netherlands, you must have a social security number (in Dutch, burgerservicenummer). This number means that you have registered with the tax authorities and the social security system. If you plan to stay longer than three months, you must register in the municipality where you live, which will issue you a social security number.
BSN (burgerservicenummer) is a unique number for everyone registered in the Personal Records Database (BRP). Everyone who registers with the BRP is automatically given a BSN.
Your BSN can be found on your Dutch passport, identity card or driving licence. You can login with your DigiD on MijnOverheid.nl to check it also. Your payslips, annual salary statements, health insurance cards and health insurance policies have your BSN on them too.
BSN (burgerservicenummer) is your tax identification number in the Netherlands (previously called SOFI number). Everyone who works in the Netherlands must have a BSN, it is necessary to settle all the formalities in various Dutch institutions.
When you register with your local municipality (for a short or long stay) you'll be assigned a citizen service number (BSN). For either procedure, you'll need to make an appointment with the municipality (gemeente) in which you live.