To treat adequately of the central mystery of Christianity -- the Incarnation, the ineffable union of the Word of God with an individual human nature -- in such a relatively small volume, is a challenge indeed. Fr. Francis Ferrier's contribution in this, another volume in the Twentieth Century Encyclopedia of Catholicism; is more than adequate. Because of the limitations of space, the author obviously had to presume that those interested in some of his references would seek basic sources for elaboration. In the case of the explanation of the ""hypostatic union"", however, the author leaves much to be desired. Once the author begins to discuss the ""human nature of the Word"" he offers in concise form the benefits of his wide familiarity with the literature on the subject. But when dealing with the ""divine"" activities as against the human ones of Christ, the author runs into the same difficulties which so many authors of this subject face -- dealing through a finite mind with an infinite subject-and the result is no more than adequate. Nevertheless, the book is a key volume in the Encyclopedia series.