: The determination of the mechanical properties governing the stability of an existing dam is complex, in particular because of the discontinuities present in the foundation and the interface between the dam and the foundation. These properties are the tensile strength, the cohesion and the angle of friction. EDF, IRSTEA, Sherbrooke University, Hydro-Québec, Clermont-Auvergne University and IFSTTAR have initiated research in order to produce data useful for understanding the failure mechanisms and to propose methodologies to assess mechanical properties in an engineering context. The results of the tensile and shear tests on concrete-rock interfaces are published in the present article. The main results can be summarized as follows. The tensile strengths obtained in tests are between 0.2 and 0.5 MPa depending on the rock type whereas a null tensile strength is usually assumed for initial calculations. The cohesion ranges between 1 and 2.5 MPa in large scale tests, as compared to 100 kPa recommended for initial calculations. These results outline the conservatism of default values and the hidden margins generally present in mechanical characteristic estimations. All the test results can be exchanged and shared with the engineers interested in the subject. The article also presents methodologies for determining the characteristics of rock discontinuities in shear and thus the tensile strength characteristics of the concrete-rock interface. Perspectives are proposed such as the characterization of the apparent cohesion of rock discontinuities and the estimation of the geometry of the dam-foundation contact by non-destructive methods.