Book cover for “Fifty Shades of Grey.” (Amazon)

Written by E.L. James — a former TV executive, wife and mother — the books began as “Twilight” fan fiction. (You can’t make these things up.) In the first book, naive and inexperienced 21-year-old college student Anastasia Steele begins a relationship with a slightly older billionaire named Christian Grey, who has a proclivity toward kinky, dominant/submissive sexual relationships.

(Buzzfeed compiled a list of the book’s 15 “best/worst” lines, if you need an introduction. Obviously, it’s NSFW.)

“Fifty Shades of Grey,” which has been described as “mommy porn” and “a guilty pleasure,” was originally released chapter-by-chapter online, and gained popularity through word of mouth. The books were first published as hard copies by an Australian publisher. The rights to re-release the trilogy were obtained by Vintage Books for “a seven-figure sum,” according to the New York Times.

The three books — “Fifty Shades of Grey,” “Fifty Shades Darker and “Fifty Shades Free” — are currently at the top of the New York Times’ best sellers list for e-books.

Deadline described the race to obtain the rights to bring “Shades of Grey” to the big screen as “feverish.” But it seems the winning studios will have to solve a pretty big problem. Namely, how will an X-rated book be successfully translated to the big screen? Should the films stick to the source material and go for an NC-17 rating? Or should they be watered down to reach a larger audience? If you’re familiar with the books, please weigh in with a comment.