If you are coming to the Netherlands to work or to study, you will need a Citizen Service Number (Burgerservicenummer -BSN). The BSN is a unique personal number which you will receive when you register with the municipality at the Expat Centre Leiden.

A BSN is required to arrange all your affairs with Dutch government agencies, therfore please make sure to keep your BSN confidental. Also after moving abroad, this BSN will always be your registration number for the Dutch government, it will be yours for the rest of your life. 
A BSN is needed to start a job in the Netherlands, enrol in an educational programme, open a bank account, use the health care system, apply for benefits and pay taxes, to name a few examples.