The citizen service number (BSN) is a unique personal number allocated to everyone registered in the Personal Records Database (BRP). Everyone who registers with the BRP is automatically given a BSN. It is used by the government, healthcare, education, and for housing and healthcare allowances. You need to apply for a BSN as soon as you arrive, you do this by making an appointment to register at the local municipality/gemeente.
Read more about the BSN here(opens in a new tab).