Marine fouling causes economical problems. Fouling diminishes the efficiency of propulsion of the ships. It enlarges the cost in fuel. Another effect is the loss in time and money because it necessitates frequent docking of the ships. These organisms increase the corrosion of metal in seawater. The damage to the timber constructions by marine borers causes renewed change of the piles. Therefore information was given about the principal fouling organisms at the Belgian coast. Some biologic aspects of the fouling were reviewed as the biotic succession by the different communities, the relation of fouling growth to local environments, the vertical zonation and the settling behavior of larvae controlled by salinity, temperature and light.