In order to achieve a better understanding of the glow discharge, different models have been developed for the different species present in the plasma. An overview of the models is given and some typical results are presented. These results include, among others, the densities and energy distributions of the plasma species, the electric field and potential distribution, the contribution of different ionization mechanisms to the ionization of argon and sputtered atoms, the relative contribution of different plasma species to the sputtering process, and the variation of the cathode dark space length and the electrical current as functions of voltage and pressure. The validity of the present models is supported by the good agreement of the calculated current-voltage curves with experiment.