Ignition systems discussed herein are those used on medium to large stationery gas fueled industrial engines. The ignition systems for these engines have developed over the years from inductive high tension unit magnetos to the modern variable timing capacitor discharge systems. The operation of a simple capacitor discharge circuit is explained. There are five parameters that describe the basic performance of an ignition system. There are secondary voltage, spark duration, energy, timing and coming-in speed. A discussion of current technology in each of these describes the state of the art.