De Ceremoniis (also spelled cærimoniis or cerimoniis) is the Latin title of a description of ceremonial protocol at the court of the Eastern Roman emperor in Constantinople. It is sometimes called De ceremoniis aulae byzantinae. Its original title in Greek is Περί τῆς Βασιλείου Τάξεως ("On the Imperial Order").
The book was written by, or produced for, emperor Constantine VII (913-959), and was partially revised or updated under Nikephoros II (963-969), perhaps under the supervision of Basil Lekapenos, the imperial Parakoimomenos.
It is a detailed description of ceremonial procedure for court functionaries, lays out how exactly they should conduct them, and addresses other matters affecting daily routines of court life in the Great Palace of Constantinople. It is therefore a manual of protocol consultation and instruction for high officials and courtiers.
One of the book's appendices is the Three Treatises on Imperial Military Expeditions, a war manual written by Constantine VII for his son and successor, Romanos II.