My collection of fiction is a little more focused than non-fiction. Most of it fits into just two large categories, with only a few leftovers.

• While some people group Science Fiction and Fantasy together as "Speculative Fiction," I choose to separate them. My Science Fiction collection contains books where science is an integral part of the story or background. I have entire shelves full of favorite authors' output: David Weber, Alan Dean Foster, Anne McCaffrey to name a few. Other books are sorted into sub-genres: hard-science SF, military SF, and so on.
• The rest of my speculative-fiction collection generally fits under Fantasy. Again, I have some pages devoted to specific authors - Tolkien, Lackey, Pratchett - and others about sub-genres of fantasy: epic fantasy, swords & sorcery, and more.
• Literature is where I put books that are generally considered "classics". Not that I have many of them;my experience with reading "the classics" has often been a feeling of "why are these considered classics at all?" Few are as good in my eyes as a good SF yarn.These are the few that passed that test.
• Mysteries are exactly what it says in the name: the mysteries I've read and liked enough to keep.
• Military Fiction is, again, exactly what it sounds like: fiction about armies and warfare.