The national Flag of Belgium contains three equal vertical bands of black (hoist side), yellow, and red; the vertical design was based on the flag of France, whereas the colours were taken from the colours of the Duchy of Brabant. When riots were starting as result of the Belgian revolution against the Dutch domination, a civil guard was established which wore the colours of Brabant. Its unusual proportions (13:15) are of unknown origin.

The flag was adopted January 23, 1831, soon after the Belgians gained their independence from the Netherlands in 1830. The flag had played an important role during the revolt, where the colours of the flag served as a reminder of an older flag with horizontal bands used during a previous revolt in 1789 in the then Austrian Netherlands. The original flag was with horizontal bars, but it was changed to vertical because of the resemblance with the flag of the Netherlands.

Article 193 of the Constitution of Belgium describes the colours of the Belgian Nation as Red, Yellow and Black instead of the order used in the above official flag.