The author is a journalist, senior correspondent for the National Catholic Reporter, a newspaper known for its progressive stance both politically and theologically. Allen has authored a half dozen books, including The Future Church: how ten trends are revolutionizing the Catholic Church and All the Pope's Men: the inside story of how the Vatican really thinks. It should be no surprise that this book is written in a clear and compelling fashion. It is easy to comprehend, even by non-Catholics, and even by non-academics. What might be more of a surprise, given Allen's background, is that this book is not driven by a progressive agenda, but represents a balanced and objective attempt to describe Catholic history and explain how the Church has arrived at its doctrine and structure. While no book under three hundred pages could hope to cover these topics comprehensively, it does provide a satisfactory introduction, including an 18 page topical index, and several dozen other books for recommended reading.

Allen's introduction reiterates the big picture that so many in the academy or the clergy often forget: that  worldwide there are 1.2 billion baptized Catholics, increasingly concentrated in the developing world, with Catholics constituting a quarter of the U.S. population  with six million converts, but there are twenty-two million ex-Catholics in the U.S. (A topic beyond the scope of this book would be the number of nominal Catholics, how they acquired that status, and what it would take to re-ignite their participation within the community.)

Allen provides the key terminology: sacraments, liturgical year, priest, deacon, bishop, curia, canon law, parish, diocese, Vatican, infallibility, beatification & canonization. Allen is not afraid to tackle thorny questions of birth control, abortion, stem cell research, same sex marriage, divorce, upbaptized infants, transubstantiation, veneration of Mary, angels & demons, the Crusades, the Inquisition, the Holocaust, the Church's management of its financial assets, and the sexual molestation scandals. One of the touchiest of these has to be how the Catholic leadership understands the position of other religions: respecting them for approaching God, but criticizing them for being "gravely defective" for not accepting the fullness offered by Jesus and His Church. One of the best things is Allen's clarity in how the Church may change its position on doctrine or ethics, or the syncretism of Catholic ritual with indigenous traditions.

Allen repeats a quote from John XXIII: "I have to be pope for those with their foot on the gas, and those with their foot on the brake." Allen's book should be appreciated by both camps, as well as by non-Catholics.