Applying for a 'BSN'
The Citizen Service Number (burgerservicenummer, BSN) is the personal code with which you are registered with the government. Although you are not officially required to apply for a BSN, it could be handy to have one for practical reasons. For example, it would allow you to open a Dutch bank account.
If you will be staying longer than four months, a BSN will be given during your visit at the THIC office. This will be arranged by the International Office.