Abstract Safe use of low lying and densely populated coastal regions depends critically on the performance of coastal structures in defending these areas against storm surges, wave attack, flooding and erosion. Continuing sea level rise and climate change (storms are becoming rougher) emphasise the need for reliable and robust predictions as higher storm surges and bigger storms may lead to flooding. Population pressures on land use in coastal regions have sometimes ignored age-old appreciation of coastal hazards. The CLASH research project EVK3-CT-2001-00058 was funded by the EU to provide “Crest Level Assessment of coastal Structures by full scale monitoring, neural network prediction and Hazard analysis on permissible wave overtopping”. One of its main objectives was to produce a generally applicable prediction method based on permissible wave overtopping and hazard analysis. This paper describes the problems related to wave overtopping and crest level design of coastal structures. Within the CLASH background, the development of a generic prediction method and its use taking into account hazards is presented.