Advancing and receding contact angles of four organic liquids and water were measured on a variety of polymer surfaces and silicon wafers using an inclinable plane. Contact angles varied widely from liquid to liquid and from surface to surface, Surface roughness was relatively unimportant. Instead, the contact angles seemed to be more closely tied to the chemical nature of the surfaces. In general, contact angles increased with the liquid surface tension and decreased with the surface tension of the solid, Several definitions were used to calculate contact angle hysteresis from the experimental data, Although hysteresis is usually considered an extensive property, we found that on a given surface a wide range of liquids gave a unique value of reduced hysteresis. Apparently, reduced hysteresis represents an intrinsic parameter describing liquid-solid interactions.