The national flag of Belgium is a tricolour consisting of three equal vertical bands displaying the national colours of Belgium: black, yellow, and red. The colours were taken from the coat of arms of the Duchy of Brabant, and the vertical design may be based on the flag of France. When flown, the black band is nearest the pole. It has the unusual proportions of 13∶15.

The Duchy of Brabant, a state of the Holy Roman Empire, was established in 1183. It developed from the Landgraviate of Brabant of 1085–1183, and formed the heart of the historic Low Countries. The Duchy comprised part of the Burgundian Netherlands from 1430 and of the Habsburg Netherlands from 1482, until it was partitioned after the Dutch revolt of 1566–1648.