The conduction of electricity through a gas manifests itself in various forms. The current in visible. self-sustaining electrical discharges may be as small as micro-amperes for coronas or as large as mega-amperes for arcs. The transformation of a gas from being a good insulator to being a good conductor of electricity occurs when electrons are liberated from neutral gas molecules and liquid or solid surfaces. The article describes the mechanisms of such electron production and the fundamental properties of the resultant discharge. Electrical discharges can be of great use to mankind or may cause serious problems; examples of both are given, as seen mainly from the viewpoint of an electricity supply industry.