The Order of Prayer in the Liturgy of the Hours and Celebration of the Eucharist 2022. An Ordo is essentially a guide for clergy to aid in preparation of the liturgy. It contains a calendar of the Liturgical year (Advent to the final day before the next Advent) and contains directions concerning the Office and Mass to be said for each day. It includes some indication of fast days, special feasts, special devotions, and devotions and feasts of particular importance to certain dioceses. The use of an Ordo dates back, in different forms, to the Middle Ages. Guides for directing and offering instruction as to the form of Mass and Office for each day of the year were among the early books printed with the invention of the printing press. Some of the earlier versions, including one from 1475, included instruction for all possible years, not one specific year. Even with the advent of the printing press, books could be costly, so disposable, annual books didn't catch on right away. The exact date of origin of the annual Ordo as is used today is not known for sure, though it seems to have grown in popularity in the 1700s. From the Preface of the Catholic Ordo, also called The Order of Prayer in the Liturgy of the Hours and Celebration of the Eucharist. This Ordo provides readers with the following: Daily Precis, Responsorial Psalm, Suggested Prayers, Intentions, Saints, Pastoral Notes.