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. 
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.