This article reviews the fundamental aspects of the dissolution of the most important oxide phases that constitute the passive films on carbon-based and stainless steels. The factors that control the dissolution behaviour of iron(III), chromium(III) and mixed oxides are thoroughly discussed. It is shown that the reactivity pattern of these oxides can be rationalized in terms of the surface complexation approach, in which adsorbed ligands bonded to surface metal ions are viewed as real chemical entities. The relevance of these basic principles to the development of formulations for chemical decontamination is also discussed.