Most studies of solids at high temperatures have concentrated on rare gases or metals. However, in the last few years, the special properties of ionic solids at high temperatures have become increasingly important, with applications to geophysics, ceramic processing, nuclear fuels, solid-state electrolytes, and so on. This volume includes a review by W Hayes and M Hutchings on some of the recent experiments, notably comprehensive work on crystals with fluorite structure, including uranium dioxide. Such experiments can be both difficult to perform and are equally difficult to interpret. There have also been striking developments in the quantitative atomistic theory of defect properties and transport. All these are studied from different aspects in the following three reviews: on anharmonic lattice dynamics using the shell model (R Ball), on the prediction of defect free energies and transport (J Harding) and on dynamical simulations of superionic conductors (M Gillan).