The aim of this paper is to examine the relation between trust and knowledge codification in the context of the implementation of an expert system in the French steel company, Usinor. The Sachem (Système d’Aide à la Conduite des Hauts Furneaux en Marche ) expert system project, which was designed to improve blast furnace control, was initiated by Usinor in the 1980s as part of a larger programme of knowledge codification and centralisation. One of the objectives was to preserve knowledge and practices the company felt might face extinction during a period of massive layoffs that threatened to disrupt the traditional knowledge transfer patterns which had hitherto been carried out primarily via an apprenticeship system...