"The oldest and strongest emotion of mankind is fear, and the oldest and strongest kind of fear is fear of the unknown." --H. P. Lovecraft
The sentence above is often quoted, but many readers aren't aware of its context. It opens this short monograph (really, a very long essay), which Lovecraft originally wrote in 1927, after a three-year stint of intensive reading, in response to the request of a pen pal, W. Paul Cook, for a historical survey of weird fiction to be published in The Recluse, a magazine Cook hoped to start. It appeared in the first issue, but that was also the only issue. It was later serialized in a fan magazine in the 30s, and Lovecraft sporadically tinkered with revisions and updates during his lifetime; but the amended version was published only in 1939, after his death, and as a free-standing book in 1945. E. F. Bleiler, himself the foremost academic critic of his generation to actually take weird fiction seriously, provides this information in the 5 1/2 page preface to the 1973 Dover reprint edition, which was the one I read. (He also contributed the handful of helpful short footnotes, and apparently the index of authors and titles.) As he notes, this was really the first serious historical-critical survey of this field, a landmark of its type, with continuing value for readers and scholars of the weird. (This, however, doesn't mean that it's an unflawed work.)
HPL organized his 106 page treatment into ten chapters. In the introduction, he defines his area of interest as the literature of "cosmic fear," that which posits or hints at mysterious realities alien to humanity and threatening towards it. (By "supernatural" in the title, he means unexplainable by the normal understandings of natural phenomena that we use in day-to-day experience.) He argues for the legitimacy of this literature as an expression of a basic and permanent part of the human psyche. The second chapter is a Eurocentric survey of prehistoric, folkloric, ancient and medieval roots and precursors of literary horror before it begins to appear in prose in the 18th century. In the other eight chapters, he provides an opinionated, and sometimes patronizing, survey of nearly all of the important, and many of the less-known, British, American, German and French authors of literary weird fiction and poetry (mostly the former) down to his own time. (He frequently summarizes the whole plots of novels, so readers should be warned that his discussion may contain major spoilers!) In some cases, such as Ann Radcliffe, he deals with writers who aim to evoke fear or horror, but who admittedly don't resort to cosmic or "supernatural" causes for it.
Because his shabby-genteel family couldn't afford to send him to college, Lovecraft had only a high school formal education; he was very well-read as an autodidact, but not being an academic literary major, he doesn't lace his essay with critical jargon. That's a plus; but he also tends to write here in the same kind of "purple prose" he used in his fiction. In the latter context, it's very powerful and atmospheric; in nonfiction, it's sometimes opaque, so with some of his sentences here describing the style or merits of other writers, it can be anybody's guess as to exactly what he means. (He also uses italics for titles both of books and short stories, apparently not being aware of the convention of using normal type and quotation marks for the latter; and he doesn't seem to be aware of the broader periodizations and historical context of Western literature as a whole as a frame for his treatment.) Generally, his meaning is clear, but in the cases where I've read the same works that he has, I don't always agree with his critical judgements, which tend to reflect his own personal preferences. For instance, he's disdainful of any morally didactic purpose in literature (while my view is just the opposite), is tone-deaf to spiritual values and concerns, and disparages the occult detective tradition just because he disliked fictional detectives. (I also have to admit that in many instances I haven't read particular writers or works that he discusses, so can't second-guess him there. He does whet my appetite for reading some of them, and introduces a few I hadn't heard of.) All of that said, though, there are a lot of times that I concur with him, and I do find some of his comments insightful and felicitous. The book also provides a window into his own literary influences; the terms in which he describes and praises particular writers like Robert W. Chambers and Arthur Machen leave no doubt as to where he got some of his own inspiration. (Not surprisingly, Poe has an entire chapter devoted to him --but I disagree with HPL as to whether Poe's horror is of the cosmic sort, and "Mesmeric Revelations" proves IMO that the earlier writer was no "materialist.")
Fans of this work have sometimes declared that it's never been superseded. Given the fact that it's dated in several respects, it frankly needs to be. But it's still a groundbreaking work with a lot of solid content, and a basic starting point for looking at an overview of this type of literature. If it ever is superseded, whoever writes the new and updated definitive treatment will be shortchanged if he/she doesn't start by reading this essay, and making use of the foundation that HPL laid here.