This dictionary has been the single most helpful work of reference that I have used in my 10 years of studying theology. O'Collins and Farrugia tend to emphasize terms that appear more often in constructive (or systematic) theology. You'll find, for example, all of the significant ancient heresies dealing with the Church's development of Christology or Trinitarian theology and ample discussion of more philosophical terms (e.g. "positivism," "empiricism" "Aristotelianism," "Averroism"). There are a number of entries for terms relating to biblical exegesis, Church history and institutions (e.g., "Crusades," "Malibar Christians"), but an adequate treatment of these fields is really beyond the scope of any portable reference work. (FYI: For a fine 1-volume dictionary of technical terms for biblical exegesis, have a look at Richard N. Soulen and R. Kendall Soulen's "Handbook of Biblical Criticism, 3rd ed., Revised and Expanded"; for an adequate 1-volume work on Christian history, there is none better than F.L. Cross and E.A. Livingstone's "The Oxford Dictionary of the Christian Church, 3rd ed. Revised and Expanded; this latter work has recently been published in a much cheaper, concise version, which is probably quite good, but I haven't perused it). In addition to these inevitable deficiencies, this dictionary would have been greatly enhanced if its authors had included bibliographic information with each entry. But in lieu of their accomplishment, this is a minor point. To my knowledge, there is no other work like this in print today, and if doing theology is your mainstay, it will certainly be one of the most used books on your shelf, regardless of your level of learning. I'll end this review with an anecdote from an introductory theology class that I taught 2 years ago, in which this dictionary was a required companion piece. After the first few weeks of class, I wondered whether students were using this dictionary and began to feel some regret for having compelled them to purchase it. Then at mid-term, I handed out an informal teaching evaluation and asked the students to rate each book they had been exposed to (4-5, I believe) from 1-10, according to how "helpful" the book had been. My undergraduate students consistently rated this book the highest. So in short, if you are thinking about buying this book, you probably should do so! (Note to professors in theology: You may want to get your hands on the out-of-print "Theological Dictionary" written by Karl Rahner and Herbert Vorgrimler for your shelves. While O'Collins and Farrugia's "Concise Dictionary" is better overall, many of the former work's entries provide complementary information).