Fan fiction, has always been popular on Internet forums -- Amazon wants to encourage fan fiction writing through its new "Kindle Worlds" program.

Kindle Worlds, which Amazon Publishing announced on Wednesday, lets authors write "fanfic" based on licensed series and sell their works in the Kindle Store. Authors will receive 35% of net sales for books of 10,000 words or more, and 20% for short stories between 5,000 and 10,000 words.

Authors will be able to submit completed works beginning in June, when the Kindle Worlds store will launch with 50 titles Amazon commissioned from successful authors including Barbara Freethy and John Everson.

Amazon's licensing program is a big first step in legitimizing fan fiction, as authors looking to sell their stories currently are forced to tread lightly or face copyright lawsuits. But signing on with Amazon means fanfic authors will have to play by Amazon's rules. The company's content guidelines for authors include six no-nos: pornography, offensive content, illegal/copyright infringing content, poor customer experience (i.e., misleading title or a poorly formatted novel), excessive use of brand names and "crossover" stories that include elements of two different series.

Still, fan fiction writers may see those items as small concessions, given that Amazon has created a platform for them to make some cash.