This Handbook contains a general survey of atmospheric discharge phenomena and of the protection devices in use. It gives the explanations in the appendices to the various chapters are necessary for an understanding of the phenomena as well as for calculating the design of protection devices. For a wider study of theory and physical phenomena, reference should be made to the numerous specialized publications. It seems best to limit the field of application of this Handbook to telecommunication lines and associated equipment. The latter also include cable and overhead lines which lead to transmitting installations, radio relay stations, etc. at high altitude, which are thus more than normally exposed. The present Handbook does not deal with the protection of the stations themselves, since such problems concern the protection of buildings against lightning and this, for transmitting stations and radio relay stations, falls within the domain of radio technique. The protection of the buildings in which the telecommunication equipment is installed is governed by the national regulations on lightning protection.