West Africa at the moment is totally absent from discussions relating to the Middle Stone Age. Sites belonging to this period have been known in this region for a long time, but their stratigraphic context has frequently been unsure or is completely lacking. As in southern Africa and in western Europe, progress in our knowledge of this stage depends mainly on the construction of a general chronological framework, preferably correlated with worldwide climatic changes and supported by absolute dates. For this reason the study of the complex of open air sites at Ounjougou has opened up a new perspective of the MSA in West Africa. Almost 30 archaeological levels belonging to the period have been identified within thick Pleistocene deposits, most of aeolian origin. Systematic recovery of OSL dates has allowed this sequence of deposits to be determinated chronologically, and the many palaeolithic occupations have thus been indirectly dated. The oldest MSA occupations are dated to the end of the Middle Pleidocene, about 150 kyrs ago. They are more numerous between 80 and 25 kyrs ago, with a particular concentration in isotopic stage 3. As usual in open air sites, the density of material within these archaeological levels is very variable, and only the lithic industries have been preserved. Apart from the frequency of occupation, the originality of this archaeological sequence resides in the diversity of these industries, which follow on one from another without any apparent logic. Techniques of manufacture (such as Levallois, discoid, blade, unipolar, or bipolar on anvill) alternate throughout the sequence, and industries characterized by bifacial foliate artefacts occur more than once. If for the most part of these industries fit easily enough within the West African MSA as a whole, there are same questions arising with regard to the diversity of technical traditions and their rapid alternation. Are there regional equivalents for this rhythm of change, does it have any particular significance in terms of the peopling of West Africa at this time, and what could have led to these rapid change?