One of the cardinal questions connected with any cultural heritage object concerns its origin. In the case of the oldest Slavonic manuscripts preserved from the 10th-11th century and still composed in the Glagolitic script of the teacher of the Slavs, Constantine-Cyril (9th c.), until recently we mostly knew only their place of discovery, but not of their previous history. In the last decade, however, two previous projects have shown that the finding place of the better part of these often fragmentarily preserved books was also their most important place of origin – St. Catherine’s Monastery in the Sinai. Obviously, this distant home of monasticism served the authors of these writings not only as a pilgrim destination, but also as a refuge at times when church politics in their various homelands (from Bohemia to Bulgaria) impeded the free practice of their ancestral literary and ecclesiastical traditions. In addition to the Sinaitic finds, however, there also exists a smaller group of Glagolitic manuscripts which were discovered in different locations of the Balkans – the most outstanding (according to style and decoration in connection with age, size and state of preservation) of them being the codices Zographensis, Marianus and Assemanianus. Their place of origin still remains an open question. The same applies to the remnants of deleted underwritings (palimpsested texts) mainly discovered in fragments of Sinaitic manuscripts. The focus of the proposed project is the investigation of the origin and later fate of all these early sources for the development of the Glagolitic and Old Church Slavonic traditions. At the same time it is necessary to further study and edit all palimpsested and other hitherto inaccessible texts which have not yet been fully deciphered. Finally, the results of those examinations must be placed into their historical context to complete our picture of the cultural history of the relevant regions. In order to achieve these objectives, humanity scholars (Slavicists), scientists (computer vision specialists, chemists, phycisists, microbiologists) and conservators will engage in inter- and multidisciplinary cooperation employing philological and historical methods of manuscript studies, language analysis and literary criticism in combination with up-to-date relevant technologies, such as Multispectral Imaging and Document Image Analysis, material investigation via spectroscopy (with soft x-ray- and visible UV-radiaton, Raman etc.) and DNA as well as the latest preservation analyses and techniques. The interplay of the different investigations will allow important new discoveries not only for the areas in question, but also the development of new methods relevant for other disciplines such as Slavic political and church history and Byzantine-Greek philology or theology, which will benefit the future exploration of any written heritage.