Radiation damage at high doses (approaching or exceeding one displacement per atom) has been studied widely in metals and alloys in view of its importance in fission and fusion reactor technology. Insulators have received less attention, but their use-actual or potential-in reactors and as host materials for radioactive waste has stimulated recent studies. Insulators present conceptual problems compared with metals: electronic as well as atomic processes may contribute to radiation damage and different sub-lattices may not be affected by radiation in the same way. Ionization damage (radiolysis) in NaCl at high doses and temperatures provides a model system where the production of metal and halogen-based defect clusters can be studied experimentally and theoretically in some detail. It also has direct practical relevance to the storage of high-level radioactive waste in salt repositories. Fast neutron damage to high doses will be sustained by insulators used in any future fusion reactors. Basic studies of the formation of voids and dislocation structures in AI,O, irradiated with neutrons, ions or fast electrons show how the processes depend on displacement dose and temperature.