Lake Baikal, in south-central Siberia, has been the focus of an international effort (the Baikal Drilling Project; BDP) to obtain continuous long cores (upwards of 100 m) from this unique rift-valley lake and to interpret the paleoclimatic history from various proxy data. As part of this effort, the clay minerals were examined by two research teams. A consistent clay-mineral assemblage, containing illite, interstratified illite-smectite, chlorite, and kaolinite as the major minerals, characterizes much of the modern sediments. The relative abundance of these minerals changes with depth in both short piston cores from various parts of the lake and in 100-m-long cores taken from the distal toe of the Selenga Delta (BDP-93).