This book presents observational studies of the earliest stages of high-mass star formation, as revealed by the Atacama Large Millimeter/submillimeter Array (ALMA). The author investigates the birth environments of high-mass stars by identifying and analyzing their immediate progenitors—dense cores embedded in infrared dark clouds. The book highlights ALMA’s capability to detect star formation signatures even in regions lacking bright mid-infrared emission, owing to its high resolution and sensitivity. It also presents a statistical study of core properties, suggesting the necessity of core growth and the discovery of core-scale infall motions that point to the role of external accretion. Based on the largest statistical sample to date, this work places observational constraints on theoretical models and offers new insights into the physical conditions that govern high-mass cluster formation.