Most analyses of industrial models assume that production systems can be distinguished from one another by the level of product variety offered by manufacturers. There are said to be two polar configurations: on the one hand mass production, characterised by a single product model under a regime of standardisation, and on the other hand ‘lean production’, suited to a regime of greater product variety (Womack, Jones, and Roos, 1990; Coriat, 1995). Indeed lean production is said to mark a return to the initial product variety of the automobile industry’s early days. Yet by the close of the GERPISA programme The emergence of new industrial models (see Foreword), a programme in which the authors of the various chapters in this book participated, it had become clear that this general hypothesis was invalid, since product variety did not in fact discriminate between industrial models. This conclusion was reached both through an historical analysis of company trajectories towards the adoption of flexible mass production systems and through an analytical approach to the principles of productive organisation inherent in different industrial models (compared over time and in terms of their contemporary diversity) which permit companies to manage product variety.