Provinces of Belgium
During the second half of the 20th century, Belgium transitioned from a unitary state to a federal state with three Communities and three Regions. As part of the state reforms, the (bilingual) province of Brabant was split in 1995 three ways: into two (unilingual) provinces (Flemish Brabant and Walloon Brabant) and into the (bilingual) Brussels-Capital Region. (The Brussels-Capital Region does not belong to any province, is not a province, and does not contain any provinces.) The two new Brabant provinces became part of the Flemish Region and the Walloon Region respectively. The remaining eight provinces became part of these regions as well, so the Flemish Region and the Walloon Region each contain five provinces.
Postal codes in Belgium
Postal codes in Belgium are numeric and consist of 4 numbers. The first digit indicates the province (except for the 3xxx numbers that are shared by the eastern part of Flemish Brabant and Limburg, the 6xxx that are shared between the Hainaut and Luxembourg province, and the 1xxx that are shared by the Brussels Capital Region, the western part of Flemish Brabant and Walloon Brabant). The more zeros though the higher the number of inhabitants of that city in the province. For example: Brugge is the capital and largest urban centre of the coastal province of West Flanders so it gets the 8000 code, the second city is Kortrijk and gets 8500. 
When writing the address, the postal code is put in front of the town name.