Shadowmarch, by all accounts I see, is pure Fantasy. Your bookstore doesn't distinguish between the two primary categories of speculative fiction. Lord Loss is horror, IMO. It's closer to fantasy than science fiction though, since it's clearly an alternate world with demons and werewolves and stuff and there's nothing I can see that's science fiction despite it being a modern society. IMO the REAL border between science fiction and fantasy is crossed by stories like Star Wars. It's equal parts technology and mysticism. Probably why it's labeled "space opera" rather than either science fiction or fantasy. Edit: Science Fiction - Science fiction is a genre of fiction dealing with the impact of imagined innovations in science or technology, often in a futuristic setting. Exploring the consequences of such innovations is the traditional purpose of science fiction, making it a "literature of ideas". Science fiction is largely based on writing rationally about alternative possibilities. It is similar to, but differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically established or scientifically postulated laws of nature (though some elements in a story might still be pure imaginative speculation). Fantasy - Fantasy is a genre of fiction that uses magic and other supernatural phenomena as a primary element of plot, theme, or setting. Many works within the genre take place in fictional worlds where magic is common. Fantasy is generally distinguished from science fiction and horror by the expectation that it steers clear of (pseudo-)scientific and macabre themes, respectively, though there is a great deal of overlap between the three (which are subgenres of speculative fiction).