Les Bossats is a prehistoric open-air site located in the commune of Ormesson, Seine-et-Marne. Its long occupation of about 30,000 years ranges from the Middle Paleolithic to Badegulian, including Mousterian, Châtelperronian, Gravettian and Middle Solutrean, approximately 50,000 to 19,000 years BP.

The site is of primary importance on several archaeological aspects. Its exceptional duration of occupation and its good conservation make it possible to establish a chrono-stratigraphic framework much more precise than that known until then north of the Loire.
Interest is particularly high for the Early Gravettian, a facies of the early Upper Paleolithic poorly known in the region; Especially since the remains of this age are among the best preserved. He also delivered the first Gravettian human fossil found north of the Loire.
It is also the northernmost Châtelperronian deposit in France and more generally in Europe - although this northern limit may only be due to a lack of research rather than the absence of sites per se.