Renewable energy which uses potential resource of the seas as their source, is a very important element of the global energetic future. Almost inexhaustible energy potential is contained in seas that cover the most of the Earth's surface, which makes renewable marine energy one of the least exploited energy sources. Technologies used during exploitation of this energy sources are very similar as inland hydro-energetic and wind-energetic energy sources, although the level of application remains lingering back. Marine energy is not greatly influencing the environment, in which sources are exploited. This is a favourable option for energy generation in ecologically endangered areas. Development of this branch of energetics, relies on the global energetic community's tendency for improving sustainable and renewable obtaining of clean energy. These thesis present theoretical elaboration of problems and conditions for exploitation of marine energy, which refers to wave energy, sea currents energy, ebb and tide energy, salinity difference energy and thermal energy. An overview was provided on the systems that are used and tested at a time, for different forms of marine energy with theirs technical and technological features, advantages and disadvantages. At the end of thesis there is an end view on possible exploitation of wave energy in Republic of Croatia.