Successful science fiction movies and TV series have always had a tendency to spawn tie-in printed books. Many movies have an accompanying novelization, usually based on an early version of the script. Some movies and TV shows produce other kinds of tie-ins too, such as episode guides and "behind the scenes" books about how they were made. These have almost vanished now, thanks to the rise of the Internet and the DVD "behind-the-scenes" documentary. But there are still a few of them around.