Abstract Research studies and case-histories of the collapse of vertical breakwaters have revealed the destructive potential of impact loads due to breaking waves and confirmed that during severe storms a large number of wave impacts can be generated of such severity as to cause the failure of the breakwater-foundation system. The problem of addressing the probability of occurrence of impact loading from breaking waves is very complicated as it involves different aspects, closely interconnected, of hydrodynamic and morphological nature. Moreover, the breaking of waves in presence of vertical breakwaters is likely to be different in character from that most usually studied which relate to the case where waves are breaking due to shoaling water depths or to a driving wind, and till now there has been very little study of wave breaking in the presence of reflection. This gave rise to studies, most of them experimental, aimed at improving the reliability of the design procedures of vertical breakwaters. The analyses of hydraulic model tests have stressed the importance of particular combinations of wave conditions, bottom slope, berm and vertical wall profile on the generation of impact loads. In this paper recent research results on the prediction of the occurrence of wave impacts on vertical structures are described and general design formulae and graphs, based on extensive bidimensional and tridimensional hydraulic model tests with random waves, are proposed. Key Words: Vertical breakwaters; breaking waves; wave impacts. 1. Introduction Vertical breakwaters are frequently employed for the protection of harbours areas around the world and, in Europe, most of them have been constructed along the Italian coasts. The reason for the success of such a structural typology, typically consisting of a monolithic vertical concrete caisson rested on a rubble mound foundation, is essentially justified by the fact that this breakwater type represents, especially in relatively deep water, a better alternative in terms of performance, construction rapidity, Prediction of Wave Impact Occurrence on Vertical and Composite Breakwaters Mario Calabrese Dept. of Hydraulic and Environmental Engineering University of Naples Federico II via Claudio 21, 80125 Napoli, Italy. Fax+39 081 5938936. E-mail calabres@unina.it Diego Vicinanza Dept. of Civil Engineering, Second University of Naples via Roma 29, 81031, Aversa, Italy. Fax+39 081 5037370. E-mail diegovic@unina.it