Coatings are widely applied to improve the durability of components. In order to understand how corrosion protection is obtained, the behaviour of coatings in aggressive environments must be characterized. Factors responsible for an increase of the susceptibility to corrosion are indentified and methods available to characterize these factors are reviewed. These are indirect methods as they do not concern the measurement of corrosion rates, nor the study of corrosion mechanisms. They deal with morphology, composition, crystallographic structure and mechanical properties of the coating.