This paper contains exhaustive analytical data on factors contributing to wear. The wear of a deformed body interacting with an absolutely rigid rough solid is considered. It is believed that wear results from the deformation of a body due to geometrical and mechanical factors and due to the adhesion bonds thereof. Three types of wear are considered: By elastic deformation, by plastic deformation, and by microcutting. The suggested criteria allow us to determine conditions which cause these types of wear to appear. It is shown that the rate of wear, i.e., the ratio of height of the worn layer to the distance of sliding at elastic contact depends on the elasticity modulus, roughness, friction coefficient, nominal pressure, rupture stress of material, and on the power exponent of fatigue curve; at plastic contact it depends on roughness, nominal pressure, hardness, destroying deformation, and friction coefficient; at microcutting—on roughness, nominal pressure, and hardness; wear at microcutting is independent of friction coefficient. The formulas deduced are borne out by experiments. These formulas may be readily modified for the case of two rough surfaces.