Low-pressure gas discharge modeling is reviewed, both from a historical perspective and for current industrial applications. An overview of the basic mathematical and physical models used to describe low-pressure discharges is given, together with a summary of the most common numerical techniques which have been adopted. Modelling of the DC glow discharge and discharges maintained by high-frequency (RF and microwave) electromagnetic fields is reviewed with illustrations of the validity of these models in predicting discharge properties and explaining and interpreting experimental results.