The ISO 19403 series specifies optical test methods for the measurement of the contact angle, for the determination of the free surface energy of a solid surface, including the polar and dispersive fractions, for the determination of the surface tension of liquids, including the polar and dispersive fractions, and for the checking of the measurement arrangement with reference materials. It can be applied for the characterization of substrates, coatings and coating materials. The applicability can be restricted for liquids with non-Newtonian rheology1). This document specifies terms and definitions and defines the general principles.