License exists in Belgium but boating around the coast or further out to sea is open to all and does not require a license... On the other hand, a boating license for recreational navigation on the Belgian inland waterways is mandatory for steering a pleasure boat that is either a minimum of 15 meters in length or is equipped with an engine and can reach a speed of at least 20 km/per hour.
An equivalent license issued by the appropriate authorities of your country is also accepted.