Tidal stream energy is a form of marine energy with significant advantages compared to other types of offshore renewables, albeit the levelised cost of energy is relatively high. Various types of foundations have been considered for prototype tidal stream generators, however the utilisation of Gravity Based Structures (GBS) seems like a promising approach to achieve cost reduction and increase the financial viability for commercial deployments. The generators are expected to be deployed onto rocky seabeds and the GBS (made of steel or concrete) need to ensure the overall stability of the structures. This research focuses on the investigation of the shearing resistance of the foundation – seabed interface materials by means of laboratory element testing. Interface tests of five different rock types (representative of sites with tidal energy potential around the U.K.) on steel and concrete were carried out under a range of normal stresses. The different properties of the counterface materials (i.e. steel, rock, concrete) allowed the investigation of the controlling parameters on the shearing resistance of steel on rock and concrete on rock interfaces. Tests results were interpreted to determine the effect of the applied normal stress, surface roughness, hardness and rock strength (UCS) on the shearing resistance of the interfaces. It was found that the relative ratios of some counterface properties (e.g. roughness, hardness) can be utilised to explain the interface shearing behaviour. A framework described by a power function has been developed to estimate the shearing resistance of rock on steel and rock on concrete interfaces, incorporating the effect of these counterface material properties.