Statistics of the causes of damage to telephone installations in various countries show that many breakdowns and faults are due to atmospheric discharges.Both overhead lines and telecommunication cables and associated technical equipment are subject to these effects. Early in the development of telecommunicationtechnique, great importance was attached to protection of overhead telephone lines (which predominated at the time) against lightning. With the growing use of telecommunication cables it became recognized that the latter are likewise subject to damage by lightning, although it was fìrst thought that a buried cable was sheltered from the harmful effects of atmosphericdischarges. This is true only for some of the phenomena occurring at the time of the lightning discharge.The importance of cable telecommunications has obliged engineers to go deeply into the physical Characteristics of atmospheric discharges and to draw conclusions for the efficient protection of telecommunication lines and associated equipment.Furthermore, many installations contain solid-state elements (transistors, diodes, etc.) which are much more sensitive than classical elements and which are liable to be damaged at fairly low voltages and currents.This Handbook contains a general survey of atmospheric discharge phenomena and of the protection devices in use.The theoretical explanations in the appendices to the various chapters are necessary for an understanding of the phenomena as weli 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 telecommunicationequipment is installed is governed by the national regulations on lightning protection