The main objectives of this paper are the analysis of the modeling problems for the dynamic behavior of moored devices for marine tidal energy harnessing and the solutions proposed for the GESMEY generator. The paper has been divided in four parts: the analysis of the energy resources and the state of the art of the technologies used for their exploitation, the description of the GESMEY generator, the modeling problems for this kind of devices and, finally, some examples of the dynamic behavior of the GESMEY generator.