In the past five years significant advances have been made in understanding the mechanism by which the bioleaching of sulphide minerals occurs. Kinetic models based on the proposed mechanism are being used successfully to predict the performance of continuous bioleach reactors. The measurement of oxygen and carbon dioxide consumption rates together with the measurement of redox potentials, has led to this further elucidation of the mechanism of bioleaching of sulphide minerals and enabled the kinetics of the sub-processes involved to be determined separately. It has been shown that bioleaching involves at least three important sub-processes. The primary attack of the sulphide mineral is a chemical ferric leach producing ferrous iron. The first two sub-processes of chemical ferric reaction with the mineral and bacterial oxidation of the ferrous iron are linked by the redox potential. The sub-processes are in equilibrium when the rate of iron turnover between the mineral and the bacteria is balanced. Rate equations based on redox potential or ferric/ferrous-iron ratio have been used to describe the kinetics of these sub-processes. The kinetics of bacterial ferrous iron oxidation by Thiobacillus ferrooxidans and Leptospirillum ferrooxidans have been determined over a range of expected operating conditions. Also the chemical ferric leach kinetics of pyrite have been measured under conditions similar to those in bioleach systems. The kinetics have been described as functions of the ferric/ferrous-iron ratio or redox potential which enables the interactions of the two sub-processes to be linked at a particular redox potential through the rate of ferrous iron turn-over. The use of these models in predicting bioleach behaviour for pyrite presented and discussed. The model is able to predict which bacterial species will predominate at a particular redox potential in the presence of a particular mineral, and which mineral will be preferentially leached. The leach rate and steady state redox potential can be predicted from the bacterial to mineral ratio. The implications of this model on bioleach reactor design and operation are discussed. Using these rate equations it is possible to predict the steady state redox potential and sulphide mineral conversion in a continuous bioleach reactor. The model successfully predicts laboratory data and is being tested against data from pilot-plant and full-scale bioleach systems. Using 16S rDNA techniques, it has been shown that in pyrite–arsenopyrite bioleach reactors, the iron oxidizer, Leptospirillum ferrooxidans and the sulphur oxidizer, Thiobacillus caldus predominate. No Thiobacillus ferrooxidans could be detected. These observations are in agreement with the predictions from the kinetics and the electrochemical mechanism of ferric leaching of sulfide minerals.