The non-stoichiometric compounds of iron sulphide named pyrrhotite (Fe1−xS) are often associated with pyrite (FeS2) in sulphidic ores and their waste products. The factors affecting pyrite and pyrrhotite oxidation are similar but the latter has received much less attention. As it is the case for pyrite, an increase in temperature has an increasing effect on the oxidation of pyrrhotite and the process follows the Arrhenius behaviour. Both ferric iron and bacteria act as catalysts in the oxidation reactions and play a significant role in the oxidation kinetics. Several spectroscopic techniques are used to study the oxidation mechanisms and products of pyrrhotite oxidation. This paper presents and discusses the main factors controlling pyrrhotite oxidation and the proposed mechanisms of oxidation under normal conditions of temperature and pressure.