Pretty Little Liars is an American teen drama mystery thriller television series developed by I. Marlene King and is loosely based on the novel series of the same name written by Sara Shepard. The series follows the lives of four high school girls whose clique falls apart after the disappearance of their leader. One year later, the estranged friends are reunited as they begin receiving messages from a mysterious figure named "A" who threatens to expose their deepest secrets. The series features an ensemble cast, headed by Troian Bellisario as Spencer Hastings, Lucy Hale as Aria Montgomery, Ashley Benson as Hanna Marin, Shay Mitchell as Emily Fields, Sasha Pieterse as Alison DiLaurentis and Janel Parrish as Mona Vanderwaal.
The series premiered on June 8, 2010 on Freeform, formerly known as ABC Family, and ended on June 27, 2017. After an initial order of 10 episodes, ABC Family ordered an additional 12 episodes on June 28, 2010. The ratings success of the first 10 episodes prompted the book series to be extended beyond the initial eight novels.
Since its debut, the series has received mixed reviews from television critics, but remained a relative success for Freeform, garnering a large fandom, primarily on social media.
On March 26, 2013, a spin-off series was announced, titled Ravenswood, but was canceled after one season. On June 10, 2014, Pretty Little Liars was renewed for its sixth and seventh seasons. On August 29, 2016, Freeform confirmed that the series would be ending after its seventh season in 2017. Filming of the series officially wrapped on October 26, 2016. The series finale was viewed by an estimated 1.41 million viewers. It had the second-highest rating of any cable TV series that aired that night. The episode was followed by "A-List Wrap Party", a live special featuring the cast and executive producer King discussing the series ending.
On September 25, 2017, Freeform announced that a second spin-off series, titled Pretty Little Liars: The Perfectionists, had been ordered, with Pieterse and Parrish reprising their roles as Alison DiLaurentis and Mona Vanderwaal respectively. On May 14, 2018, Freeform picked up the series for a 10-episode first season, set to air in 2019. In a 2018 panel, Parrish said that some plot points created in Pretty Little Liars will be resolved during the spin-off.