Built in the 6th century by order of Emperor Justinian, the Monastery of Saint Catherine in the Sinai desert preserves the oldest Christian monastic library with an uninterrupted history. This Greek Orthodox Monastery houses a significant collection of manuscripts in the world, including a large number of palimpsest manuscripts (over 170). Eleven different languages are attested in their erased layers as "scriptiones inferiores": they reflect the long history and the multicultural nature of the Sinai shrine. This book lies at the intersection of palimpsest studies and the investigation of the Byzantine Greek Euchologia (prayer books), with an additional focus on the history of the Sinai library. This study offers the first inventory of the Greek palimpsests preserved at the Monastery of Saint Catherine, including a list of newly identified "membra disiecta sinaitica." The second part contains the detailed description and historical analysis of three selected Sinai Euchologia (Sin. gr. 960, Sin. gr. 962, Sin. gr. 966) written on recycled parchment, which have never been studied with regard to their "scriptiones inferiores". The collected material contributes to our knowledge of the history and development of the Sinai collection of manuscripts over the centuries.