This book introduces what sclerotia grains are, and where and how they exist in soils, by compiling the results obtained from the studies on fungal sclerotia formed by Cenococcum geophilum (Cg) and related species, the visible black small grains persistent for a few thousand to ten thousands of years in forest soils and sediments. The chapters contain the results and discussions on the ecological distribution and regulating factors, characteristics, and function of Cg sclerotia grains, carried out by researchers from soil geography, soil science, soil microbiology, physiology, forestry, analytical chemistry, environmental chemistry, material science, and related disciplines. The anatomy of sclerotia grains in soil was realized in terms of interdisciplinary joint researches, which resulted in deepening understanding of the ecological function of the mesoscale organic component in soils. This book covers the natural history of sclerotia in soils, pedo-sclerotiology.