The paper describes the present position regarding some components used in electrical instruments from the aspect of reliability and functional suitability under severe working conditions. Most of the components discussed are considered from the point of view of the Services, where a high standard of performance is required even under extreme climatic conditions. Details are given of the shortcomings of some of the present-day components and of the effort which is being directed to overcome them by the exploitation of new materials, new processes, improved design and better methods of manufacture.In addition to the commonly used components, such as resistors, capacitors and transformers, mention is also made of a precision variable inductor, and Sections dealing with meters, electronic valves and quartz-crystal units have also been included.