Strength and ductility are the important characteristics which govern the hot working properties of a material. This paper describes test methods for measuring hot workability and then discusses deformation and fracture mechanisms in hot working. Particular emphasis is laid on the correlation of strength and ductility data in simple materials in terms of dependence on strain rate and temperature. Suitable correlations enable the identification of basic parameters controlling deformation and fracture processes. With complex materials, these correlations cannot be applied due to the occurrence of precipitation reactions and the presence of inclusions and second phases having markedly different strength and ductility characteristics.