This collection of thirteen essays arises from a session held at the Twelfth International Economic Congress in Madrid (August 1998). The historical case studies presented here demonstrate the complex dependence of technological forms on shifting background conditions like market changes or institutional developments. Recent research on the key themes addressed in this volume has shown the path-dependent aspects of technological trajectories and change. Directions taken in the past may have long term effects: in the selection of techniques for example, earlier events, sometimes dominated by chance elements, could give rise to a single technological outcome, even a suboptimal one, and exert important influences on the future developments of processes and products. Path-dependent views are a challenge to the neo-classical theory of rational choice. The contributions scrutinise the conditions in terms of trajectories - firm or industry specific in some essays, regional or national in others - explaining stability or reorientation. Les treize textes reunis dans ce volume sont issus d'une session tenue dans le cadre du XIIe Congres International d'Histoire Economique a Madrid en aout 1998 qui a aborde la question