This paper contains a review of the improvements and growth of colonial telecommunication services during the last 30 years or so, combined with a study of the measures that have been found necessary to overcome the special problems in telecommunication engineering that result from tropical conditions. It is based on experience in British colonial, protected and mandated territories, which lie mainly within the tropical zone. There has been previous mention of these problems in papers by the late Mr. Llewellyn Preece1and by the late Mr. R. W. Weightman.2Mr. Weightman was for many years associated with colonial telecommunication services, and it is appropriate that tribute be paid here to the large share he had in solving many of the problems discussed herein. He described in his paper the services in Canada, Australia, South Africa and New Zealand. Since then there has been much progress, and the telecommunication engineers of the Dominions must now be left to speak for themselves. The present paper is therefore concerned only with the colonial, protected and mandated territories under the direct control of the Mother Country. The paper is divided into four main sections as follows:(1) General requirements for telecommunications in colonial territories.(2) Characteristics of tropical climates.(3) General design of external plant.(4) Design of apparatus and components for tropical conditions.