This volume presents a comprehensive overview of Mt. Kusatsu-Shirane, one of the most active volcanoes in Japan in terms of persistent release of volatile as volcanic gas and hot springs. The unexpected eruption of Kusatsu-Shirane volcano on January 23, 2018, caused human damages. It shed light on the difficulty of the prediction of phreatic eruptions, whereas motivated studies on schemes for volcano monitoring, research and disaster mitigation of the dormant volcanoes. This book includes the past and on-going research on the Kusatsu-Shirane volcano with varieties of disciplines such as seismology, geodesy, geomagnetism, geochemistry, petrology, and social science research on reporting of the eruption in 2018.