Abstract Systematic investigation of deep-sea sediments started with the Challenger Expedition in the late nineteenth century. The findings of this expedition have been central for the recognition of the deep-sea sediments in mountain ranges. These sediments were seen as deposits formed in the deepest part of geosynclines. Progress in marine geology in the mid-twentieth century and the discovery of seafloor spreading culminated in the theory of plate tectonics. Plate tectonics provided the global framework for ocean history and for the understanding of deep-sea sediments in mountain ranges. With the inception of the Deep Sea Drilling Programme (DSDP), a new phase in deep-sea sediments research was started. Open-marine deposits including deep-sea sediments were classified as ‘pelagic sediments’, a term with no depth connotation in the definition. Pelagic sediments were discovered as archives for ocean history. The Mesozoic with its peculiar climate became a promising target for this new field of palaeoceanography. Most exciting were findings of Cretaceous black shales in all the major oceans and the recognition of globally occurring ‘Oceanic Anoxic Events’ (OAE). Mesozoic black shales serve as proxies for peculiar conditions in palaeoceanography and they record perturbations of the global carbon cycle, possibly triggered by changes in atmospheric CO 2 concentrations and recorded in the carbon-isotope signature of marine carbonates. The combination of isotope geochemistry and sedimentology resulted in a step from palaeoceanography to palaeoclimatology. New developments in stratigraphy provided the time frame for unravelling climate history with a high time resolution of 10 4 years or less. Future investigations of pelagic sediments will be based on an ‘earth system’ approach, and new geochemical and palaeontological tools will be used in the investigation of pelagic sediments as archives of past climate and environment.