This study seeks to clarify the date, nature, and probable origin of a noted breviary currently preserved as part of a greatly misunderstood manuscript, Lucca, Biblioteca Arcivescovile, MS 5. It argues, from a close study of the manuscript's hands and codicological structure, that the breviary of Lucca, Bib. Arc. MS 5 was once an independent manuscript, not part of the rest of the liturgical material now appended to it, but created sometime between 1125-1150. The notation of the breviary, taken together with the breviary's primary hand and curious red neumes added by the rubricator, suggests that the breviary may have been compiled by a scribe from Chartres, probably a cantor. No obvious feature of the breviary connects it to the Crusader Latin Kingdom of Jerusalem, but painstaking comparative study of the breviary's contents show that its liturgy was drawn from diverse European sources; this points to the breviary's composition outside of Europe. Methodical study of the breviary's liturgy in the context of known manuscripts representing the liturgy celebrating in the Patriarchate of Jerusalem in the twelfth century demonstrates that breviary's creators drew upon the early twelfth century use of the church of the Holy Sepulchre in Jerusalem; this limits the breviary's production to somewhere in the Patriarchate. Further comparative analysis of the breviary's liturgy shows that the breviary does not represent the pre-1149 office of the church of the Holy Sepulchre itself. Instead, by excluding other major churches of Jerusalem for various reasons as the breviary's probable point of origin, this study argues that the breviary of Lucca, Bib. Arc. MS 5 most likely represents the use of one of the cathedrals of the patriarchate. Finally archaeological and prosopographical research, and especially a study of the career of Fulcher of Angoulême, Archbishop of Tyre, is used alongside the contents of the breviary's liturgy to argue that out of all the cathedrals of the patriarchate, the breviary of Lucca, Bib. Arc. MS 5 most likely represents the use of the cathedral of Tyre as it existed sometime between 1135-1150, though the breviary itself must have been copied for the personal use of someone associated with the cathedral, probably the cantor.