Wetting studies usually involve measurement of contact angles as primary data. When a liquid does not completely wet a substrate (usually a solid), a contact angle is formed. Contact angle is a quantitative measure of the wetting of a solid by a liquid. It is a direct measure of interactions taking place between the participating phases (gas/liquid/solid or liquid/liquid/solid). The contact angle is determined by drawing a tangent at the contact where the liquid and the solid intersect. The shape of the drop and the magnitude of the contact angle are controlled by the three interaction forces of interfacial tension of each participating phase (gas, liquid and solid). It is often necessary to distinguish between the Static (Equilibrium) Contact Angle (θe) and Dynamic Contact Angles (DCA) i.e. Advancing Contact Angle (θa) and Receding Contact Angle (θr). When θr ¹ θa the system is said to exhibit contact angle hysteresis. Contact angles can conveniently be measured with optical tensiometers based on drop shape analysis and traditional mass based tensiometers. The Theta and Sigma series tensiometers from Attension provide state-of-the art instrumentation for both types of techniques for determining static and advancing contact angles. More