The study of ocean sediment cores has made it possible to document past climate variability beyond the instrumental period, that is, since direct measurements of climate variables such as water or atmospheric temperature are available. In paleoclimatology, or the study of past climates, scientists use indirect methods, called “proxies”, to reconstruct past climate conditions. This chapter attempts to cover first a brief history of the MNHN oceanic collection, second, the development of coring techniques and, finally, the types of proxies currently used to reconstruct sea temperature, salinity and CO 2 concentration, three parameters that are very sensitive to climate change. There are several coring techniques, but most of the cores in the oceanic collection are from “calypso” type piston corers, derived from the Kullenberg corer, invented in 1947. Although knowledge of foraminiferal biology and geochemistry has made significant progress in recent years, much work remains to be done to make these new proxies more robust.