During the past 50 years tools for predicting wave overtopping of sea defense structures have continuously been refined. However, developers of wave energy converters have raised questions about how to predict the overtopping of structures with layouts significantly different from those of sea defense structures. Optimization of structures utilizing wave overtopping for the production of electrical power has been ongoing throughout the last decade. It has been established that the information available in the existing literature is insufficient to describe overtopping of such structures. The present thesis describes investigations conducted against this background. The development of guidelines for calculating overtopping discharges for a wide variety of slope layouts is presented. Both structures with single and multi level reservoirs are examined. All geometries have been subjected to a wide range of sea states. Overtopping slope layouts resulting in substantial energy content in the overtopping discharges have been pointed out. The influence of various geometrical parameters, such as slope shape, shape of guiding walls, draft and crest freeboard, on the overtopping discharges has been investigated. The effect of using overtopping reservoirs at multiple levels has also been quantified. The emphasis is generally on optimizing the overtopping with respect to maximizing the potential energy in the overtopping water. Based on the experimental data expressions for predicting wave overtopping discharges, and vertical distribution of overtopping above the slope are proposed. The overall hydraulic efficiency of wave energy converters, based on the overtopping principle, can be 20 -35 % when a single reservoir is used, and up to 45 - 50 % for a structure with reservoirs at 4 levels.