Citizen service numbers are called BSNs - which stands for burgerservicenummer. You'll need to apply for a BSN within five days of your arrival by making an appointment with the local municipality office.   You can book most appointments online, and you will need to bring your paperwork with you; they will advise what documents are required. Your BSN is vital since you'll need this to open a bank account, buy health insurance, or access medical care.   A BSN is required of every person living in The Netherlands.