Volcano-sedimentary cores recovered from Pleistocene Palaeolake Olduvai by the Olduvai Gorge Coring Project (OGCP) provide a high-resolution record for reconstructing climatic and environmental contexts of hominin evolution. Approximately 612 m were recovered from four cores from three drill sites across the basin depocentre through scientific drilling, and these have yielded unprecedented data that substantially extend the Olduvai record both temporally and spatially. Results from multiproxy analyses based on sedimentological, mineralogical, isotopic, and geochemical measurements, along with analysis of organic matter and microfossils, backed up by new 40Ar/39Ar dating, palaeomagnetic reversal analysis and tuff fingerprinting, provide detailed palaeoecological and palaeoenvironmental data, and stratigraphic resolution adequate to provide context for the palaeoanthropological records from outcrops. In this Special Issue we present the first phase reporting of the core results, which establishes a new stratigraphic and palaeogeographic framework upon which palaeoenvironmental and palaeoanthropological data can be contextualized. The cores revealed thick intercalated lakebeds below the Bed I Basalt and the even older Naabi Ignimbrite, more than doubling the thickness of the known Olduvai stratigraphy. Seismic studies suggest that the sedimentary sequence contained in the lake's depositional sump extends even further back in time, perhaps back to ~2.5 Ma, nearly 500 kyr older than the deepest strata exposed in outcrop. From stratal characteristics, we deduce that the palaeolake was deeper, more permanent, and longer-lived within the lake sump than previously thought, at least until the Masek Beds (before ~0.82 Ma), although frequent phases of total or nearly total lake emptying/drying were detected, and the lake depocentre was at times filled by volcaniclastic fan progradation during periods of intense volcanic activity in the neighboring Ngorongoro Volcanic Highlands. Furthermore, biogeochemical evidence supports our interpretation of the lake history, and documents abrupt transitions in terrestrial vegetation, aquatic biota, and lake dynamics on a Milankovitch and sub-Milankovitch scale, which potentially exerted complex influences on hominin-exploited palaeolandscapes. This work revises the longstanding view of the basin history and transforms the scientific debate about the environmental conditions under which hominins evolved in the Olduvai Basin.