Interest in oxide ceramic coated metals, in particular aluminium alloys has increased in recent years. Treatment processes such as plasma electrolytic oxidation (PEO) are more frequently being exploited commercially to provide hard wearing chemical and thermal barriers. This has led to an interest in the failure of such coated systems and the development of duplex systems, those using mechanical pre-stressing, for increased fatigue life. Failure mechanisms in these systems are often assumed without testing thus limiting our ability to optimise. The influence of interfacial shear strength is crucial to the understanding of the failure mechanism in both simple treatments and duplex systems. This paper demonstrates a method for evaluating the interfacial shear strength in PEO coated 2024 as part of a simple tensile test. Direct optical methods have been used to measure surface strains at macro and micro scales and the shear lag method applied to infer the interfacial bond strength. The influence of coating on the general stress-strain behaviour is examined and the interfacial shear strength evaluated.