This is the book which made C.S. Lewis' reputation as a critic of medieval and renaissance literature; in the original, medieval, sense, it was the "piece" that marked his transition from Apprentice to Master. It was first published in 1936, and has been reprinted many times. (I have 1960s copies of Oxford's 1958 "Galaxy Book" paperback edition; the cover of the recent Oxford Paperback is a great improvement.) As originally written, it covered the development of allegorical narrative from late classical antiquity to the Elizabethan poet Spenser's "Faerie Queene," with particular attention to the "Allegorical Love Poems of the Middle Ages" (the working title).
Unhappily for the book's long-term reputation, Lewis was persuaded to add to the planned text an earlier summary of modern theories of "courtly love" in medieval life and literature. Lewis himself noted that this theoretical construction did not quite fit the texts he analyzed in detail, and the whole approach is now regarded as at best problematic, and by many as simply wrong. Since Lewis presented the material with unusual clarity and wit, however, he has come to be treated as an authoritative source on "Courtly Love" theory by some, and attacked as such by others.
The rest of the book, being based on original studies of primary sources, retains much of its value. Later textual studies and shifts in crticial theory have only slightly diminished its value, and his discussions of such now-obscure writers as Martianus Capella remain among the most inviting of introductions. Lewis' treatment of "The Romance of the Rose" is still illuminating (and the point of departure for many recent re-considerations). His chapter on "The Faerie Queene" is regarded by some competent scholars as the foundation of modern study of the unfinished epic.
Although Lewis never looses sight of the entertainment value of many of the works he discusses (and some of them never had any), he is concerned to show that they addressed real problems of human behavior and emotions, and their presentation in narratives. Norman Cantor (not, on the whole, a great admirer) reports from first-hand experience that the book helped make the study of medieval romances respectable in academic circles. My own reading of the secondary literature (pre- and post-Lewis) brought me to a similar conclusion.
It is probably of interest to note that, according to Lewis himself, the "Chronicles of Narnia" did NOT arise from his studies of allegory, and that their allegorical implications arose spontaneously in his mind. One has to wonder whether he would have written "The Allegory of Love" differently after, rather than before, those experiences.
Serious students of English literature, and medieval literature in general, will find "The Allegory of Love" more than worth their time. So will those who simply enjoy reading Arthurian literature, and several other types of story. For many who are familiar only with Lewis the fantasist, or Lewis the Christian apologist, it will open new perspectives.
[Extended Addendum, October 21, 2013]
[This is one of my earliest reviews, which I've revised slightly to suit other editions of the book. However, it has been attached to a new Kindle edition of "The Allegory of Love" (Illustrated and Annotated by Glenn Langohr), about which I feel I should make some comments.]
[Although it is nice to have this too-long out-of-print book available again, and at a very nice price, there are some drawbacks to the edition. Footnotes are missing entirely, including those which provide original texts for quotations which Lewis translates in the main text. Some of those translations were into verse, which is at least partly printed as if prose, concealing Lewis's considerable skill. (The combination also conceals his general accuracy at catching the sense and tone of, e.g., Ovid.) The "annotations" and illustrations attributed to Mr. Langohr consist of captions to a photograph of Lewis and some stock pictures of medieval and Pre-Raphaelite (or similar) art. The captions inform the reader what the book is about, not about the illustrations or artists; they amount to an extended blurb, rather than a contribution to understanding the text.]
[HarperCollins has announced another edition, as a Kindle (and, I think, other ebook) for November 2013. This will cost over twice as much, which is still a good price compared to used copies in good condition. Presumably, HarperCollins, a major publisher with a long Kindle catalogue, tried to do the job right.]
[In the meantime (short as it is), or for those who can't afford it, there are, from time-to-time, copies readable on-line or as pdfs, put up, I think, mainly by English Departments (and the like), frustrated that their students have not had ready access to a notable book.]