A detailed knowledge of the physical and mechanical characteristics of rocks, on the surface and underground, and their methods of movement are necessary in engineering design. Those which are of greatest interest in dealing with the problem of supports and super-incumbent rock are ultimate strength, density, permeability and elastic and viscoelastic module. Various systems of identification and classification have now been developed relating to "intact rock" and "in situ rock". These are discussed, together with some of the instruments needed for determination of induced and inherent stresses.