Equations of state for solids under strong compression

Various approaches for the representation of equation of state data for sol ids under strong compression are discussed. The theoretical background for reasonable extrapolations to higher pressures and higher as well as lower t emperatures is described. The distinction between ideal, regular, and anoma lous behaviour allows to gain deeper insight into the electronic changes oc curring in various solids under strong compression. The discussion of exper imental data for various regular solids leads finally to an estimate of the accuracy obtained in the present realisation of a practical pressure scale based on equation of state measurements.