Christine Chataigner. Methodological reflexions on problems posed by the characterisation of obsidian. Obsidian exchange occurred over long distances during prehistoric periods. Only analysis of the chemical composition of obsidian seems to be a relevant method for retracing the routing of this volcanic glass and the identification of its sources ; macroscopic attributes such as colour and texture can vary within the same flow. Chemical analyses have been used for the majority of obsidian provenience studies, but recently several problems have come to light, namely the difficulty in distinguishing between certain sources, the variability existing within one source, and differences in geochemical composition between geological and archaeological samples. The very similar case of ceramic provenience research shows that a reliable reference collection is essential, and that the basic data from chemical analysis must be complemented by other information of a technological or geochemical nature.