The notions of line roughness as a more detailed characteristic of the solid surface and the roughness of a three phase contact line, which may be caused by both surface roughness and its microheterogeneity, were introduced. The general principle accounting for the effect of roughness in thermodynamic relationships was formulated. As an example, the generalized Young equation accounting for the roughness of the three phase contact line and possible difference in the surface roughnesses of dry and wetted surfaces was derived. The Wenzel equation was generalized to the case of rough surfaces.