When my young colleagues, Jean Lemaitre and Jean-Louis Chaboche invited me to write a few introductory lines on the occasion of the publication of their work Mécanique des Matériaux Solides (Mechanics of solids materials), I very willingly acceded to their request as an expression of trust and friendship, even though on one hand, the aim of the present work is made abundantly clear by the title and the introduction, and on the other, the well-deserved fame of the authors is quite sufficient to attract and retain the attention of readers.

The originality, I would even say the identity, of this book becomes apparent only if we place it within the evolution of the scientific subjects during the last few decades. In fact, it is part of a triple current whose recent developments it assimilates and integrates. First of all, it borrows from continuum mechanics and thermodynamics the conceptual framework and methods which, starting with a few simple concepts, allow construction of a great variety of phenomenological models necessary for describing the extremely varied behaviour of solids. Secondly, it collects, rearranges, and above all, takes advantage of the observations, schematic representations, and empirical laws which generations of engineers have used with imagination and perspicacity in guiding and accomplishing their projects. Finally, it provides an inventory of physical phenomena, especially those observed at the microscopic, molecular or atomic scale, the scale at which events determining and explaining macroscopic behaviour occur.