The utilization of marine currents for power production offers a sustainable option to augment traditional power technologies and enhance the expansion of renewables. The marine current resource is potentially large and could generate a significant part of the European Union's electricity requirements. Before the installation of marine prototypes, specific trials are necessary to evaluate the behaviour of each system and the ability to exploit tidal or marine currents. This paper presents experimental campaigns carried out on marine energy converter systems under METRI II program performed in the Ifremer free surface hydrodynamic water tunnel. Two of them concern horizontal axis marine current turbine systems: a “classical” pile-mounted tidal turbine concept and a fully submerged machine in deep water. The third concept is an innovative marine current and wave energy system based on Venturi principle from a submerged pipe network. The results presented provide useful information for the hydrodynamic characterization of marine energy converter systems, their design and for the validation of numerical studies.