The Euchologium Sinaiticum is a 109-folio Glagolitic Old Church Slavonic canon euchologium. It contains parts of the liturgy of the St. John Chrysostom, and is dated to the 11th century.
The manuscript was found in the monastery of Saint Catherine's Monastery, Mount Sinai in 1850 by the Russian archimandrite Porfirij Uspensky, and there it's still kept today excepting the three folios taken by Uspenskij and N.P. Krylov to Saint Petersburg, Russia. Among the Sinai manuscripts discovered in 1975 is a 28-folio fragment of the Euchologium Sinaiticum.
It was first published by Czech L.Leitler in 1882 in Zagreb. In the edition Patrologia Orientalis (t. XXIV, fasc. 5, 1933, p. 605-802 and t. XXV, fasc. 3, 1939, p. 487-617) it was published by J. Frček. Slovene Slavist R. Nahitagal published it in Ljubljana photographically in 1941, and in 1942 in Cyrillic transcription. Recent edition has been by I. C. Tarnanidis: The Slavonic Manuscripts Discovered in 1975. at St. Catherine's Monastery on Mount Sinai (Thessaloniki, 1988).
Researchers emphasize that the manuscript is a collection of diverse prayers of different origins: some of them are scribed to the pre-Cyrillo-Methodian Salzburg mission, and for others it's being claimed that they represent Eastern-rite missal fragments. We don't know much of its language: nasal vowels are well-preserved, there is no notation of palatalness in syllabic sonorants r and l, strong yers are sometimes preserved, and sometimes vocalized (ъ > o, ь > e), weak yers are sometimes omitted, Jagić's rule is confirmed etc.