D. R. Bensen, the editor at Pyramid Books in the early '60s responsible for a number of their more interesting releases, was also the editor of this anthology out of Unknown Fantasy Fiction, later Unknown Worlds (in an attempt to drag in more sf readers)...and this slim anthology has become easily Bensen's best-known single work, and the best-remembered anthology out of John W. Campbell's fantasy magazine, a title probably even closer to that editor's heart than his sf magazine Astounding was (that magazine later entitled Analog, as it still is known today). For a relatively unadulterated sense of what an issue of Unknown was like, as Jerry House reminds us in comments, check out the issues of the magazine and the one-shot market tester Street and Smith issued in the late 1940s online at the UNZ.org project.
At left is the original edition's rather decent, if text-heavy, cover, and below is the less impressive 1970 reprint exterior (courtesy Bill Crider and his continuing series of back and front covers of paperbacks...note the clever misspelling of Fredric Brown's name on the back cover of this volume). In 1978, Pyramid having been bought by Harcort, Brace, Jovanovich, the line was redubbed Jove Books, and Jove put out an edition with a genuinely ugly, pseudo-pulp cover that had nothing to do with the kind of covers Unknown specialized in...and that cover is rather hard to find online, at least I couldn't this morning. That, however, is the edition I bought (when it and I were new), with Bensen's brief new introduction, appended to the original brief introduction, being the major reason to seek out this last edition (so far).
The 1970 reprint rather grandly suggests that these are the best stories published in the best fantasy magazine that has ever been...and while you might find a number of people agreeing with the second half of that clause (including Isaac Asimov in his preface), relatively few people would agree too strenuously with the first phrase...Bensen was making a point of collecting good, but largely overlooked, stories from the highly picked-over pages of the magazine, and succeeded...glance at the index below, and it's hard to go too far wrong with most of these contributors...but subsequent anthologies from Unknown that were less afraid to include the chestnuts are a better indication of why the magazine, which specialized in the kind of impudent (but not completely lighthearted, as Asimov notes) contemporary fantasy written by Thorne Smith or H. G. Wells, whose dictum that only one miracle per story should be allowed was followed pretty closely, the kind of fiction that has in the last decade or two has often been tagged "urban fantasy"...and the magazine was founded in part to house the kind of near-science-fictional paranoid speculation of such work as Eric Frank Russell's Sinister Barrier.
But Unknown ranged pretty far afield, from Fritz Leiber's best early work (including the novel Conjure Wife, the definitive "urban fantasy" "Smoke Ghost," and the first published stories of Fafhrd and the Gray Mouser, the sword and sorcery anti-heroes who were easily the next step beyond Conan and even beyond C. L. Moore's contributions to the form...and which John Campbell bought, reportedly each time with the puzzled query as to why Farnsworth Wright at Weird Tales wasn't buying them instead (a very good question, and probably more to do with Wright's many blind spots than anything else, even if most of the best F&GM stories would come in later years--"The Bleak Shore" collected here is a good example of the early stories). "Yesterday was Monday" is a typically well-worked out paranoid "behind the scenes of reality" story from the young Theodore Sturgeon, who, even more than Leiber, was able to do his best early work in the pages of this magazine; Henry Kuttner's "The Misguided Halo" is similarly an example of Kuttner's deftness with the single humorous fantastic element introduced into an otherwise mundane situation. L. Sprague de Camp's "The Gnarly Man" is a fine example of the almost-sf content of the magazine, depending just a bit on magic-science in positing the legal trouble faced by a nearly immortal Neanderthal in the turn of the 1940s US; H. L. Gold's "Trouble with Water" is simply the best story I've read by Gold (and many others suggest the same), a busy writer before World War II who channeled his war-damaged psyche and considerable talent and energy into editing the revolutionary and often brilliant Galaxy Science Fiction and Unknown-like Beyond Fantasy Fiction in the 1950s. Manly Wade Wellman, Fredric Brown, Robert Arthur (ISFDb says, in this case, in collaboration with Fredric Brown, uncredited), Anthony Boucher and the others are represented with fine examples of their contribution to the magazine (and Arthur and Boucher would, in their subsequent editorial efforts as well, seek to publish similar material to that which Unknown and, increasingly, Weird Tales under new editor Dorothy McIlwraith would publish)...which, after being folded by Street and Smith in the face of WW2 paper restrictions on all publishers, lived on as a stronger thread of science-fantasy in Campbell's theoretically all-"hard" sf magazine, which would also explore, increasingly, fringe science in both fiction and supposed (at times) nonfiction contents (crackpottery would be mixed in with utterly responsible nonfictional pop-science coverage in Astounding and Analog throughout Campbell's career and at times beyond; long-term fanzine and fiction-magazine editor George Scithers would note as early as the turn of the 1960s how badly-researched even some of the attempts at sober science articles were, in interesting distinction from Analog's less-"hard" sf rivals, Galaxy and The Magazine of Fantasy and Science Fiction, which at the time had regular and scrupulously researching/self-correcting columnists in Willy Ley and Isaac Asimov, briefly supplemented by Ted Thomas, respectively).
For more of today's books, please see Patti Abbott's blog. My review of the sequel anthology, The Unknown 5, which Bensen edited and saw published in 1964.
From the Contento index:
The Unknown ed. D. R. Bensen (Pyramid R-851, Apr ’63, 50¢, 192pp, pb)
7 · Foreword · Isaac Asimov · fw
11 · Introduction · D. R. Bensen · in
13 · The Misguided Halo · Henry Kuttner · ss Unknown Aug ’39
31 · Prescience · Nelson S. Bond · ss Unknown Oct ’41
43 · Yesterday Was Monday · Theodore Sturgeon · ss Unknown Jun ’41
63 · The Gnarly Man · L. Sprague de Camp · nv Unknown Jun ’39
85 · The Bleak Shore [Fafhrd & Gray Mouser] · Fritz Leiber · ss Unknown Nov ’40
97 · Trouble with Water · Horace L. Gold · ss Unknown Mar ’39
119 · Doubled and Redoubled · Malcolm Jameson · ss Unknown Feb ’41
137 · When It Was Moonlight · Manly Wade Wellman · ss Unknown Feb ’40
153 · Mr. Jinx · Robert Arthur · ss Unknown Aug ’41
171 · Snulbug · Anthony Boucher · ss Unknown Dec ’41; reprinted F&SF May ’53
187 · Armageddon · Fredric Brown · ss Unknown Aug ’41