Belgian domicile starts at the municipality that matches your street, not a city brand. In Flanders you book the gemeente; in Wallonia and most of Brussels you book the commune. The Brussels-Capital Region alone has nineteen separate communes, so an Ixelles lease is useless if you try to register in the City of Brussels office next door.
Where do you register, and how soon?
Book the population or foreigners service for the address on your lease or host declaration. Bring identity papers, proof you may occupy the home, and any residence authorisation you already hold. Language at the counter follows the language area: Dutch in Flanders, French in Wallonia, and French or Dutch in bilingual Brussels, depending on the commune's practice and your choice where both are offered.
FPS Interior guidance for a change of address says you must declare the new main residence within eight working days of moving. Many newcomers are told to start first registration soon after arrival for the same reason: the commune needs your principal address on file. That domicile step is separate from tax registration and from joining a mutualité / ziekenfonds (compulsory health insurance fund).
EU, EEA and Swiss citizens who will stay more than three months also start the registration-certificate file at the same commune. From 1 September 2025, an Annex 19 (Bijlage 19) application for an EU registration certificate must be a complete file at the first visit: proof of EU citizenship plus proof of status such as work, self-employment, studies, sufficient means, or family link. Incomplete files are not accepted under the Immigration Office (IBZ) rule. Non-EU arrivals often report with passport, visa or single-permit decision, and housing proof; their card sequence differs, but the address check still sits at the commune of the real home.
What is the residence check and national number?
After you declare the address, local police usually run a contrôle de résidence / woonstcontrole (residence check) to confirm you actually live there. A positive check lets the municipality enter you in the waiting register or foreigners' register as your status requires, then complete National Register recording. Only then is your eleven-digit national register number finalised for banks, employers, and public services. It is not a separate PPS-style application you file elsewhere.
You may receive interim papers while the check or Immigration decision is pending. Do not invent a second home for convenience: a failed check delays the number, the residence card, and every service that depends on both.
Common misconceptions
Registering in "Brussels" is not a single window. The nineteen communes keep separate appointment systems and document lists, and Antwerp or Ghent gemeente rules do not transfer to Schaerbeek or Etterbeek.
An Annex 19 file is also not the same as a casual address update. Since September 2025, EU citizens cannot leave status evidence for a later three-month top-up when requesting the registration certificate; the commune expects the complete pack when the application is lodged.
Summary
Pick the exact commune or gemeente of your principal residence, declare the address promptly, and prepare for the police residence check before the National Register entry is complete.
EU movers should arrive with a complete Annex 19 file if they need a registration certificate, while non-EU movers follow their visa or single-permit path into the same local address process. The national register number comes out of that Belgian domicile chain, not from a separate number office.
Sources
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