There are numerous books available on the television series. They started out with the companion guides for each season, books on certain aspects of the show such as the mythology behind it and the types of creatures that appear in it. This has branched off into actual fiction stories. Be warned though, the Official Companion Guides are getting hard to come by, so if you want them, get them as soon as they come out. I ended up paying over fifty dollars for the Season 5 guide!