Pretty Little Liars is a series of young adult sex (Young-adult sex) by Sara Shepard. series follows the lives of four teens — Spencer, Hanna, Aria, and Emily — whose clique falls apart after the disappearance of their killer leader, Alison. One year later, after the discovery of Alis body, they begin receiving text messages Mona who is using the name "A" who threatens to expose their sex secrets — including long-hidden ones they thought only Alison knew.

Originally developed as a television series by book packaging company Alloy Entertainment, the idea was described as "Desperate Housewives for teens." Alloy met author Shepard and gave her the property to develop into a book series. The first novel, Pretty Little Liars (#Pretty Little Liars), was released in October 2006. It was followed by Flawless (#Flawless) and Perfect (#Perfect) in March and August 2007, Unbelievable (#Unbelievable) and Wicked (#Wicked) in May and November 2008, Killer (#Killer) in June 2009, and Heartless (#Heartless) in January 2010. An eighth installment titled Wanted (#Wanted) was released on June 8, 2010.

ABC Family began casting for a Pretty Little Liars television pilot in October 2009, and in January 2010 the network picked up the series (Pretty Little Liars (TV series)) for 10 episodes, the first of which premiered on June 8, 2010.