This sci-fi television series about teen aliens, their love lives, and high school, was based on a series of YA novels called Roswell High by Melinda Metz (who would later become a staff writer on the TV adaptation). You may recognize the female lead, Shiri Appleby, now starring as Rachel Goldberg on Lifetime's critical darling UnREAL.
Sweet Valley High
Sweet Valley High aired for four seasons in the mid-90s on Fox and UPN. The series on which it was based, Sweet Valley High, was created by Francine Pascal and written by Pascal and an enormous team of ghostwriters. SVH was a massively popular book series and spawned numerous spin-off series. There are hundreds of books taking place in the Sweet Valley universe. It's no wonder there are constant rumors of a reboot for the under-performing original TV series!
Pretty Little Liars
Sara Shepard wrote this book series of the same name. While the TV series diverged significantly from the book series, Shepard's novels gave ABC Family what is truly their biggest hit to date with the massively successful Pretty Little Liars.
The Lying Game
This series, with a very similar name to Pretty Little Liars and airing on the same network (ABC Family), was also written by Sara Shepard, the PLL scribe. Unfortunately, this later show (based on a book series of the same name) was not nearly as successful as its sister prorgram – it only lasted two seasons.
Again proving that supernatural YA is one of the richest sources for TV shows, Freeform (formerly ABC Family) snatched up this show based on the YA series The Mortal Instruments by Cassandra Clare. The book series is hugely successful. The TV adaptation is still in its infancy, and producers have taken a huge gamble re-adapting it after the massive flop of its 2013 movie adaptation, The Mortal Instruments: City of Bones. Here's hoping the TV format lends itself better to this universe.