At a parish a few weeks ago, I invited the people who had come for the Lenten talks to raise any questions they had about the coming Missal. There are two questions that keep coming up: "What book is that?" and "Will it involve the lectors?"
The two questions really do go together.
"The Roman Missal" is the official title of the book containing the prayers for the Mass. You'll recognize it as the "altar missal," which currently goes by the name "Sacramentary." (A Sacramentary is the book that has all the prayers and readings necessary for a particular sacrament.) With the new translation of the texts, we are also getting a stricter translation of the title of the book. (Most of the other language groups have been calling it the "Roman Missal" all along.)
The content of the Missal is divided into roughly four sections:
The Order of the Mass is the basic framework, with standard prayers and responses. (This part includes the various Eucharistic Prayers.)
The Proper of Time includes the specific prayers for a particular day in the liturgical year or for particular needs in the Church. A full set includes the Entrance Antiphon, Collect (opening prayer), Prayer over the Gifts, Communion Chant and the Prayer after Communion. (In Lent, we will now also be getting a special prayer of blessing at the end of each Mass; this is one of those truly new things in the new missal.) "Proper" means "specific to" or "belonging to" and is used here in the sense that the Mass for, say, the 5th Sunday of Lent is truly distinctive and belongs quite "properly" only to that day in the liturgical year.
The Proper of Saints contains the specific prayers for the feastdays of the saints and blesseds that are celebrated in the area covered by this edition of the Missal. The U.S. edition has the Mass prayers for our own citizen-saints, like Elizabeth Seton and Katharine Drexel, whose feasts would not be celebrated in, say, the Philippines or some other English-speaking nation. Conversely, those nations will have saints and blesseds of their own. But we all will celebrate the feasts of certain saints who are especially signficant on a world scale.
The Commons: You could call this a section of "general" Mass prayers, divided according to category. There are Mass prayers (complete sets, as in the Proper of Time) for significant events like the anniversary of the Dedication of a Church; in honor of Our Lady; general prayers that fit the bill for the feast of a martyr (or a group of martyrs), a Pope or a saintly lay person (perhaps the Proper of Saints will have only the first prayer, the Collect; the Commons fills in for the rest).
The "General Introduction" of the Roman Missal (known as GIRM) was released and implemented several years ago (remember?)--that covered the rubrics dimension. What we are getting come Advent is the rest of the book that we read the Intro to already.
The readings, meanwhile, for all those specific days and saints, as well as all those general or "common" needs and saints are all in the Lectionary. So the lectors can breathe easily this time. (We got the revised lectionaries earlier in the decade, remember?)