In the Prologue to The Lord of the Rings, Tolkien spends a considerable amount of time relating information "Concerning Hobbits." One thing he tells us is that not all hobbits are the same. To say that not all Catholics are the same would be a vast understatement. Starting from the top, the first distinction (not division) is that between Western Rite and Eastern Rite Catholics. I happen to be Western Rite, but that doesn't make me any more or less Catholic than those who are Eastern Rite. A "rite" is specifically what it says: an outward ritual of worship, not a set of beliefs. As far as I know, what I say in this book applies to both Eastern and Western Rite Catholics. But, although I've read Eastern Rite books and attended Eastern Rite liturgies, I don't know that form of Catholicism from the inside, so I don't make any absolute claims in that regard.
I was raised in an American family that was primarily German-Catholic, but my paternal grandmother was Irish-Catholic (and my paternal grandfather's family was, of all things, English-Methodist, although he personally became Catholic). Throughout my adulthood, I've been involved in Polish-Catholic, Italian-Catholic, Mexican-Catholic, and multiple Irish-Catholic, German-Catholic, Czech-Catholic and "American melting-pot"-Catholic households, and learned about Carmelite, Franciscan and Jesuit spirituality along with a bit of unconscious assimilation of Augustinian theology. What fascinates me more than the differences are the similarities all share in the way of looking at life and the world. In this essay collection, of course, we're trying to understand J.R.R. Tolkien's Catholicism, which was Western Rite, so that's our focus. It was also English, so the ways that Catholicism is practiced in, say, South America or Africa, and the differences in nuance we would find in those places, won't concern us directly. Since I'm assuming that many of the people reading these essays will be American, I do spend some time contrasting American ways of looking at things with Tolkien's English viewpoints; this becomes important when looking at different forms of Christianity, especially because evangelical Christianity as we know it today is primarily an American construct while Catholicism comes from a more European mindset (such as Tolkien's).
Above all, Tolkien was a traditional, orthodox Catholic. Those two adjectives don't necessarily go together. There are those whose beliefs are so traditional that they end up being "more Catholic than the pope" and putting themselves outside orthodox Church teaching. Although Tolkien didn't think the Second Vatican Council was necessary, and wasn't happy with many of the changes that had come from it by the time he died in 1973, he considered accepting them to be part of his loyalty to his faith, so always remained orthodox. On the other hand, there are plenty of non-traditional Catholics who are completely orthodox in their beliefs and practices. I'm much less traditional than Tolkien was, but I certainly consider myself orthodox.
Surprisingly to some people, on a lot of subjects (creation and evolution, as an example) Catholics have a wide spectrum of what official teaching "allows" us to accept. If you're personally acquainted with even one Catholic, there will almost certainly be places in these essays where you'll find yourself thinking, "But that's not how [insert name] looks at it." That doesn't necessarily mean one or another of us - or a third Catholic who sees things from a different angle - is wrong. Like Tolkien's various characters, each of us comes from a particular background and has been affected by a specific set of experiences as well as our own innate personality, all of which will affect how we understand the mystery of faith. In the boxed quotes from various Catholics that are sprinkled throughout these pages, you'll find people who would disagree with each other on a lot of issues (and have heated arguments on some of them). But, as I said in the first couple of paragraphs on this page, although there are surface differences there's a shared foundation. In fact, arguments among Catholics are almost always about choosing the course that's most true to our fundamental beliefs - not about those fundamental beliefs themselves.
Unless I specifically mention myself or another individual or group, "Catholics" in this book is meant to refer to those with beliefs and outlooks similar to Tolkien's. J.R.R. Tolkien was a complex mix of orthodox Catholic Christian, traditional Edwardian Englishman, World War I veteran, Oxford graduate and professor, philologist, storyteller, friend, orphaned son, husband and father. All of those elements come into play throughout LotR. In this book we'll be concentrating on the first, which Tolkien himself considered the most important influence not only on himself as a person but on his writing (cf. letter #212).