This book centers on a Greek text that was likely compiled in Constantinople, in 1105, for use in one of the monasteries located there. The book consists of a liturgical psalter, containing the fixed structure (the ordinary) in both the Greek original and in English translation, as well as a description of the hours themselves. The extensive commentary explains the development of the divine office, and the particular history of the translated manuscript, while brief notes clarify and explain, in a way suitable for non-liturgists, the more-technical aspects of the divine office. Based on a single dated manuscript, the book presents the first, fullexample of the daily structure of monastic hours as they were celebrated at a time when services had reached a degree of maturity. The book, by presenting the ordinary of the office, compliments recent work on the propers of the office, and thus helps to complete our picture of the medieval monastic office in Byzantium.