Hitherto theoretical findings on the mechanism of anodic oxidation, structure of anodically oxidized aluminium and models of the oxide layer growth are reviewed. In the modelling, the layer growth, electrochemical reactions at the oxide - electrolyte boundary and the effect of chemical dissolution were investigated. The result of the studies is the creation of a model coating, which consists of the metal, oxygen and electrolyte anions. On the basis of the model, the total amount of the oxide formed and also the amount of the porous oxide can be calculated. Though the anodic oxidation of aluminium is widely used in industry, basic research in the field is still timely.