The term destructive corrosion is used here in the sense of corrosion which proceeds to the point of causing an item of equipment to fail, requiring that it be replaced. The principal adverse environments include marine locations and industrial areas with polluted atmospheres. For underground installations, adverse environments include polluted and corrosive drainage, flood and ground waters. The electro-chemical nature of most corrosion is emphasized in a brief review of elementary corrosion theory. The various forms of corrosion likely to be encountered in CATV equipment are described, and typical causes are discussed. Sulfur dioxide and chlorides are pinpointed as the most corrosive of the atmospheric constituents. Various locations are compared in terms of severity of corrosion. Examples of equipment-related corrosion are illustrated and discussed. Corrosion testing and evaluation concepts are reviewed. Preventative design, testing, installation and operational principles are suggested.