The Sinai manuscripts comprise the oldest and most important Christian monastic library collection. Of its 3,300 manuscripts, two-thirds are in Greek. The rest are principally in Arabic, Syriac, Georgian, and Slavonic, through there are other manuscripts in Polish, Hebrew, Ethiopian, Armenian, Latin, and Persian. The New Finds correspond to these languages, and are stored adjacent to the library. The library also contains an important archive, containing letters, account books, charters, and other documents.

Most of the manuscripts are Christian texts for use in the services, or to inspire and guide the monks in their dedication. But others are of an educational nature, such as classical Greek texts, lexicons, medical texts, and travel accounts.

The most famous manuscript is the fourth century Codex Sinaiticus, of which the monastery retains twelve pages and some twenty-four fragments. Next in importance is the Codex Syriacus, a palimpsest, the upper writing dating to AD 778, with the underwriting dating to perhaps the fifth century. This is one of only two manuscripts in the world that preserve the text of the Old Syriac translation of the Gospels.

The monastery has some manuscripts written on papyrus, and a large collection of Greek, Arabic, and Turkish scrolls. The ancient library of Sinai still exists in its original context, as the library of a living community. This association gives an added dimension to each of the manuscripts and early printed books, as they witness to the life of prayer and services that has been maintained here for over seventeen centuries.