This paper describes theoretical and experimental work carried out in the Admiralty Signal Establishment, and at the same time includes all the relevant material that the authors have been able to extract from German reports. It was decided to carry out this investigation when it became known that considerable importance had been attached to dielectric-rod aerials in Germany during recent years. The material of German origin is taken mainly from a translation by the authors of a paper by Mallach of the Vierjahresplan Institut für Schwingungsforschung, Berlin.The fundamental principles governing the radiation characteristics of dielectric rods are considered, and brief reference is made to other dielectric aerials.