It is a special pleasure for me to introduce the English translation of the book by Jean Lemaitre and Jean-Louis Chaboche. Readers will find this an ambitious book written in a bold and adventurous style. I had the good fortune to spend four months as a visitor at the Laboratoire de Mécanique et Technologie at Cachan in 1983. It is evident that the book reflects the dynamic and refreshing style of research at this laboratory. The aim of the book is to answer the important question of how the mechanical properties of materials are affected by complex loading histories and how this behaviour in turn affects the performance of engineering components. The approach is global. Theoretical formulation is combined with discriminating experiments and the computational power of the computer to define and calculate the factors which affect the life and performance of engineering components subjected to severe loading conditions. A great merit of the approach is its ability to be constantly improved. Incremental improvements in constitutive laws, for example, are easily introduced as are efforts which help to bridge the physical processes within the material and the macroscopic behaviour observed in experiment. By this means research and development effort can be well coordinated and gaps of knowledge become more clearly identified. While the properties of metals attract most attention the importance of the general approach is illustrated with reference to other materials such as concrete and polymers.