Oxides are formed on the surfaces of most metals we use today when they are exposed to an environment suitable for oxidation. The formation of these oxides usually has negative effects that cause severe corrosion problems detrimental to the operation of electronic devices, but it can also have positive effects in that a protective oxide layer that prevents further penetration of oxygen into the material may be formed. Therefore, understanding the effect of oxidation in metals plays an important role in the advancement of modern science and technology. In this paper, we will review the conventional theory of oxidation and present a state-of-the-art model of oxidation based on recent discoveries.