One complication of publishing is that books don't always appear with their intended titles. A famous case is Alfred Bester's The Stars My Destination, whose differently edited British edition became Tiger! Tiger! – and stayed that way for decades. This split personality was finally cured in 1996 by combining the best of both texts as The Stars My Destination; see the latest UK SF Masterworks edition. At last antihero Gully Foyle's catchphrase "I kill you filthy" appears as written, rather than toned down for sensitive Brits as "I kill you deadly" ...
Crossing the Atlantic the other way, Christopher Priest's A Dream of Wessex was rebranded in America as The Perfect Lover, something which still makes him wake up in the small hours and cringe. More predictably, another Priest SF book switched titles in France, with Inverted World becoming Le Monde Inverti – which seemed fine until sniggering French friends told him that, idiomatically, he'd published a novel called The Gay World.
This discouraged Priest's plans for a sequel to be titled The Inverted Sea, or in French La Mer Invertie. As he wailed in anguish, "I can't call a book The Lesbian Horse!"
When US author Ursula Le Guin's fantasy The Beginning Place appeared in Britain as Threshold, reviewers complained that an evocative title had been replaced by a dull one. The miffed British editor retorted that Gollancz had faithfully used Le Guin's title – it was the US publisher who'd opted for something more fantasy-like.
In the same way, Donald Kingsbury's Courtship Rite, a Dune-like eco-saga set on a horribly hostile planet, became the more science-fictional Geta in Britain. "A novel with the same number of letters as Dune!" It's a fond legend of fandom that if an SF editor got his hands on the Old and New Testaments, they'd be published as War God of Israel and The Thing With Three Souls.
The general rule seems to be, "make it sound more sci-fi". So A.E. van Vogt's The Beast became Moonbeast in the UK, and Fredric Brown's memorable The Lights in the Sky Are Stars turned into the frankly boring Project Jupiter. One unusual reason for a change is amnesia: John Barnes's Apostrophes and Apocalypses (US), or Apocalypses and Apostrophes (UK), happened because the author himself couldn't remember which way round it went.
Sometimes a title causes problems with prudes. I used to write essays for the American SF magazine Thrust, whose editor eventually renamed it Quantum because his distributors and newsagents were mysteriously convinced that Thrust sounded like raunchy, top-shelf material, to be read one-handed. Although Harlan Ellison bravely accepted Kurt Vonnegut's story "The Big Space F*ck" for his anthology Again, Dangerous Visions, reviewers of the book were somehow nervous of mentioning this one, and it hasn't been reprinted much ...
The same anthology had a contribution by cartoonist Gahan Wilson whose title couldn't even be pronounced – it was just a graphic blob. Greg Bear caused the same confusion by calling a novel /, pronounced "Slant" rather than "Stroke" or "Slash", and publishers insisted on putting Slant on the jacket in addition to the real title.
An obscure fear of pronouncing John Sladek's The Müller-Fokker Effect ensured that few people ever dared to order it in W.H. Smith's. D.G. Compton's hardback publishers found it even tougher to get orders for his classic title Hot Wireless Sets, Aspirin Tablets, The Sandpaper Sides of Used Matchboxes, And Something That Might Have Been Castor Oil – and so this was nervously altered to Chronocules for the paperback.
One of SF's cruellest name changes happened to Brian Stableford's novel War Games, whose plot culminates in shock revelations about the real motives of a seemingly minor character who's a genetically enhanced "optiman". So, to keep this narrative surprise well and truly under wraps, the US publisher retitled the book Optiman.
My favourite example of the industry's arcane title-changing habits is the offbeat SF novel which author Edmund Cooper called Kronk. (It features a raven who says "Kronk," you see, far more plausible than a raven saying "Nevermore.") The publishers vetoed this, although they wouldn't say why. After days of desperate thought, Cooper came up with an alternative that they would accept. Which is why, to the author's eternal bafflement, Kronk appeared as Son of Kronk.
Speaking of strange titles, David Langford just wrote an entry for the forthcoming "Thackery T. Lambshead Pocket Guide to Eccentric or Discredited Diseases". Yes, really.