Coming to live in Belgium means going through a number of processes in the commune of residence. Normally, foreigners staying more than three months on Belgian soil are considered "residents". They are then subject to procedures that require fulfilling various formalities, both for the resident himself, as well as his partner and children.
You must own a valid passport or identity card from your country of origin and go and register in person at the commune where you plan to stay within eight working days, starting from the date you entered the country. To register you will need three passport photographs and pay a charge of between 4,96 and 19,83 ¤ (this varies between communes). The commune will then provide a certificate (temporary permit valid for three months). The foreigner will also have to prove they have enough financial means to meet their everyday needs.
If the stay here lasts less than one year, the commune offices also require that you submit a request for residence. If residence is granted, the commune delivers a carte de séjour (blue card) valid for five years and places the foreigner in their population registers. This blue card must be renewed either when it expires, or the photo no longer resembles the person, or if it is stolen, lost or destroyed and only if the person concerned was in Belgium at the time they needed to renew their identity card. You must bring the out-dated card or declaration of theft, loss or destruction with you to ask for a new one.