The conversion of solar energy into chemical or electrical energy in inorganic photoelectrocatalytic systems is based on an ef¢cient collection of photogenerated charges under nanodimensioned semiconductor-metal Schottky type junctions in contact with the reacting electrolyte. The metal phase is separated from the semiconductor by a stabilizing ¢lm consisting of a thin dielectric or semiconducting oxide, which protects the underlying light absorber from (photo)-chemical attack. A method to achieve this type of interfaces is by using an electrochemical treatment, sometimes referred to as surface conditioning including chemical or electrochemical etching, anodic or cathodic passivation, and metal deposition steps. In this chapter some fundamental aspects of these different steps will be described and illustrated with practical examples.