At the Royal Radar Establishment work has been done on electronic components, constructional techniques for equipments, including microminiaturization and cooling methods, for many years, and the article summarizes recent work in these fields. In microminiaturization techniques maximum attention is being given to the solid-circuit approach, with microcircuit on 2D being developed to obtain experience with film components. Circuits using all-silicon components have been constructed using transistor fabrication techniques and this technology is being expanded and the performance of solid-circuit components evaluated. Complete units are being built up similar to the Texas Instruments "Solid Circuit" units. Most of the work on flat-plate or 2D circuits has been done on 0·6-in. square glass substrates, and resistors of evaporated nickel chromium using "in situ" copper masks also evaporated have been successfully made and evaluated. Evaporation of dielectric materials for capacitors has not been so successful and a comprehensive programme of research into the stresses and strains developed in thin films, measurement techniques for accurate deposition and the study of initial stages in the nucleation and growth of thin films using radioactive tracer techniques, are all being carried out. Films have been made inside an electron microscope of the actual growth and nucleation processes of thin films. Ferromagnetic films have been made and the work is described. Transistors for microminiaturization work have been fabricated, initially following the work of Diamond Ordnance Fuse Laboratories in U.S.A. but later using hermetically sealed constructions 0·125 in. diameter × 0·040 in. deep. Microcircuits using evaporated components are also being assembled in tube envelopes as a means of protection and sealing. Reliability problems have been studied at R.R.E. for many years and many analyses of faults occurring in equipments are given in the paper. A special range of "reliable" or "special quality" tubes and components is being developed and the stages in this programme are given. Results of a mass-testing evaluation of fixed resistors are detailed and some recent component developments are described, particularly some new miniature relays. The life and performance of components at excessively high temperatures is summarized and work on liquid-cooling techniques is described in some detail, including proposed cooling and construction of microminiature assemblies. U.K. military experience with wrapped joints is described and the development of new miniature wrapped joints for use in connecting microminiature assemblies is given.