"Every one of these articles provides valuable insight into the various traditions familiar to Tolkien, and from which he drew as he developed his personal mythology over the decades." -- The Historian
A solid collection of articles on various sub-topics of Tolkien's relations with myth, particularly his sources and his aim of creating a mythology. There are several very good essays on the Finnish _Kalevala_ as an influence. Tom Shippey's essay on the _Edda_ and _Kalevala_ is one of his best, and a fine example of his typical clarity of style. Several of the reprinted articles, notably Catherine Madsen's essay on natural religion and Kathleen Dubs' on Boethian philosophy, are quite thought-provoking. Andrew Lazo's essay on the Kolbitar, precursor to the Inklings, is repetitive in sections but includes a good deal of very interesting material. Also noteworthy are the papers on oaths and oath-breaking by John Holmes and on Beowulf by Alexandra Bolitineanu. All in all, a useful collection.
Let me start by confessing I haven't read this work. From the description it seems that Tolkien is given credit for the genre his work became part of. First of all, the genre of fantasy was "invented" by George MacDonald, a Scots preacher, about a century before The Hobbit was published. George MacDonald was the first to borrow from or rework ancient or medieval religious systems, which are described currently as "mythology." They are not "true" in the sense that the life, death, and resurrection of Jesus Christ is true. These occultic practices truly were heartfelt worship of earthly powers, such as demons of the trees (dryads), Lilith, and especially of Baal and Asherah, known by different names throughout the ages (such as Zeus and Saturn). We know these "stories" are part of the deception that continues to turn minds away from the ultimate power in the universe, the Inventor whose work is either glorified for what it is or perverted into what it is not. The term "mythology" is an invention, but what it describes is the "powers, the principalities, and the rulers of this present darkness" (Ephesians 6:12). Proceed with caution.