50 Shades of Grey, which started out as Twilight-inspired fan fiction, raised a few copyright questions that didn't stop it from selling millions and millions of copies. But when a work is more directly based on another author's creation -- using the same characters and setting, for instance -- the legal hurdles can be greater.
That doesn't stop readers from writing their own spinoffs anyway: The largest fan fiction site, FanFiction.net, hosts millions of free stories.
I hope this helps book authors to be able to work with these subjects of fan faction. It seems to me that anyone who can write will really find a niche that they can write about here.
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