This chapter introduces the basic properties of rock, discusses commonly used experimental procedures and explains how to interpret data from lab tests. The specific gravity is a dimensionless number, which is used to compute other rock properties such as porosity and density. Density of rock is the ratio between the mass of rock sample and its volume. Pores have a considerable effect on mechanical, especially strength properties of rock. A small amount of porosity can have a significant effect on rock deformation under stresses. The water content indicates the amount of water in rock. The unconfined compression test is conducted on cylindrical rock specimens to obtain the strength properties of rock. Unlike soil material, rock generally fails at small strain, indicating brittle behavior. Engineering practice indicates that rock tends to fail or fracture at the proportional limit of elasticity or somewhat beyond it very near the yield stress.