This guide presents the matrix of occupations and exposures to free crystalline silica dust developed by the Department of Occupational Health (DST) of the French Institute for Public Health Surveillance (InVS) and the Joint Research Unit for Epidemiology and Surveillance in Transportation, Occupational Health, and the Environment (Umrestte). It also provides technical information on occupational exposure to these dusts. For all jobs considered to be exposed in France from 1947 to 2007, exposure is assessed by period and according to criteria of probability, frequency, and intensity of exposure detailed in this technical guide. This matrix, accompanied by a presentation brochure, is available on the InVS website (Matgéné thematic dossier, www.invs.sante.fr/surveillance/matgene/index.htm) in several versions of national and international classifications of occupations and sectors of activity. (R.A.)