This book offers the first comprehensive study of how Jesuit libraries were created, organised, and used across early modern Europe and throughout the overseas missions. Drawing on a broad range of archival and printed sources, including administrative records, lending registers, internal regulations, visitation reports, and personal correspondence, it reconstructs the daily management of collections and the reading practices within Jesuit institutions. By reconstructing the concrete gestures through which books were selected, classified, consulted, and circulated, and by showing how rules were followed, stretched, or ignored, the study exposes the procedural backbone that supported Jesuit teaching, scholarship, and institutional order. It also proposes a structured method for approaching the cultural and social history of these libraries, offering a new way to interpret the wider Jesuit knowledge system.