Belgium is a federal state and is composed of three communities, three regions, and four linguistic regions. Two out of the three regions each comprise as well each five provinces, making a total of ten provinces. Belgium also comprises 589 municipalities. These are the five most important subdivisions of Belgium, as laid out into the Belgian constitution (as far as the first four subdivisions are concerned) and law (as far as the municipalities are concerned). Other less important subdivisions include for instance the electoral districts and the police districts.

Four of these five most important subdivisions have geographical boundaries: the regions, the linguistic regions, the provinces and the municipalities. On the contrary, the division by communities is neither territorial nor demographic. Belgian official communities do not refer directly to groups of people but rather to a division of the political linguistic competencies of the country (although people from a linguistic demographic non-institutional community often identify themselves with the institutions).
The three regions are the Brussels-Capital Region, the Flemish Region and the Wallon region.
The three communities are:
- the French-speaking Communauté Française ("French Community")
- the Dutch-speaking Vlaamse Gemeenschap ("Flemish Community"); and
- the German-speaking Deutschsprachigen Gemeinschaft ("Germanophone Community").
The four linguistic regions are the French language region, the Dutch-language region, the bilingual region of Brussels-Capital and the German-language region.
Brussels-Capital Region
Main article: Brussels-Capital Region
The Brussels-Capital Region (Brussels Hoofdstedelijk Gewest in Dutch, Région de Bruxelles-Capitale in French, Die Region Brüssel-Hauptstadt in German) or Brussels Region is centrally located and completely surrounded by the province of Flemish Brabant and thus by the Flemish Region. With a surface area of 162 km² (0.53% of Belgium) it is the smallest of the three regions. It contains Brussels, which acts both as federal and regional capital, and in total 19 municipalities. Its official languages are both Dutch and French. The Brussels Capital Region contains only one administrative district, the Brussels Capital District. However, for many administrative and juridical purposes (e.g. electoral purpose), it forms a district with surrounding Flemish areas (something considered by some as contrary to the Belgian Constitution).
Although many believe that the capital of Belgium is the City of Brussels municipality, the Belgian Constitution makes it clear that the capital of Belgium is Brussels in the broad meaning of the term (cf. Art. 194 and 166 of the Constitution).
Flemish Region
Main article: Flanders
The Flemish Region or Flanders (Vlaams Gewest or Vlaanderen in Dutch) occupies the northern part of Belgium. It has a surface area of 13522 km² (44.29% of Belgium) and is divided into 5 provinces which contain a total of 308 municipalities.
The official language is Dutch but French may be used for administrative purpose in the so-called "municipalities with linguistic facilities" around the Brussels Capital Region and on the border with Wallonia.
Brussels, which is geographically not part of the Flemish Region though considered by some as part of Flanders for all its Flemish inhabitants and local institutions, is also the capital of Flanders. The Flemish Region has no institutions on its own and is, as a political and administrative concept, something rather theoretical. Its competencies were transferred to the unified Flemish institutions that combine both regional and community competencies. As a result, the Flemish region has not a single civil servant of its own, no legislative council etc. It is therefore the unified institutions that exert all its power and competencies (see also: Vlaams Parlement). And, as the Flemings from Brussels are just as well Flemings as the others, it became a purely internal choice of the Flemish Community in Belgium to establish its capital in Brussels.
- West Flanders (West-Vlaanderen in Dutch)
- West Flanders has a surface area of 3151 km² (23.30% of Flanders; 10.33% of Belgium), and is divided into eight administrative districts which contain 64 municipalities.
- East Flanders (Oost-Vlaanderen in Dutch)
- East Flanders has a surface area of 2991 km² (22.12% of Flanders; 9.81% of Belgium), and is divided into six administrative districts which contain 65 municipalities.
- Antwerp (Antwerpen in Dutch)
- Antwerp has a surface area of 2860 km² (21.15% of Flanders; 9.38% of Belgium), and is divided into three administrative districts which contain 70 municipalities.
- Flemish Brabant (Vlaams-Brabant in Dutch)
- Flemish Brabant has a surface area of 2106 km² (15.57% of Flanders; 6.91% of Belgium), and is divided into two administrative districts which contain 65 municipalities.
- Limburg has a surface area of 2414 km² (17.85% of Flanders; 7.92% of Belgium), and is divided into three administrative districts which contain 44 municipalities.
See also: List of Flemish municipalities
Walloon Region
Main article: Wallonia
The Walloon Region or Wallonia (Région Wallonne or Wallonie in French) occupies the southern part of Belgium. It has a surface area of 16844 km² (55.18% of Belgium) and is also divided into 5 provinces which contain a total of 262 municipalities. Its capital is Namur.
The official languages are French and German (only used in nine eastern municipalities near the German border, which were "given" to Belgium after WWI), though Dutch may be used for administrative purpose in the so-called municipalities with linguistic facilities on the border with Flanders.
- Hainaut has a surface area of 3800 km² (22.56% of Wallonia; 12.44% of Belgium), and is divided into seven administrative districts which contain 69 municipalities.
- Walloon Brabant (Brabant Wallon in French)
- Walloon Brabant has a surface area of 1093 km² (6.49% of Wallonia; 3.58% of Belgium), and contains only one administrative district with 27 municipalities.
- Namur has a surface area of 3664 km² (21.75% of Wallonia; 11.99% of Belgium), and is divided into three administrative districts which contain 38 municipalities.
- Liege has a surface area of 3844 km² (22.82% of Wallonia; 12.58% of Belgium), and is divided into four administrative districts which contain 84 municipalities.
- Luxembourg has a surface area of 4443 km² (26.38% of Wallonia; 14.54% of Belgium), and is divided into five administrative districts which contain 44 municipalities.
See also: List of Walloon municipalities