The Indologist, librarian and bibliographer Dr. Johannes Emil Otto Klatt (1852-1903) dedicated his life primarily to the study of the historical records of the Jainas. He left behind the handwritten English manuscript of his monumental Jaina-Onomasticon, an almost completed 5338 page long bio-bibliographical index of proper names of Jaina authors, texts, and place names, with excerpts of biographical information. Klatt's contemporaries praised the manuscript as one of the landmarks of modern scholarship in this field, and today, the encyclopedic compilation is still without parallel. It represents a substantial but untapped source of information for the yet unwritten social and literary history of Jainism in post-canonical, and especially in early modern and modern periods. In making previously inaccessible bio-bibliographical materials available in a structured form, the Jaina-Onomasticon provides a foundation for the historical and sociological study of the Jaina tradition in the pre-modern period. At the same time, the text offers valuable insights into the fluid state of knowledge among leading scholars of the 19th century confronting a flood of entirely new information from different sources, and opens up enhanced possibilities for studying the interactions between European academics and Indian informants during the colonial period. The long-overdue print edition of a recognized classic in the fields of Indology and the History of Religion will be an indispensable source of reference for Jaina Studies and South Asian History in general.