Pretty Little Liars is an American mystery teen drama television series created by I. Marlene King, which aired on Freeform from June 8, 2010 to June 27, 2017, based on the novel series of the same name written by Sara Shepard, lasting 160 episodes over seven seasons. Set in the fictional Rosewood, Pennsylvania, the plot follows five best friends whose secrets are consistently threatened by the anonymous "A", who begins harassing them after the disappearance of their clique leader. Troian Bellisario, Ashley Benson, Lucy Hale, Shay Mitchell, Sasha Pieterse, and Janel Parrish lead the ensemble cast, alongside Holly Marie Combs, Ian Harding, Bianca Lawson, Laura Leighton, Chad Lowe, Nia Peeples, Tyler Blackburn, and Andrea Parker.

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. The series premiered to mixed reviews from critics, but garnered positive reception from critics during subsequent seasons, with the acting and tone garnering particular praise, while the series' plot holes were scrutinized. It was a worldwide viewership success, garnering a large fandom. The series finale was viewed by an estimated 1.41 million viewers. It had the second-highest rating of any cable television series that aired that night but received a lukewarm reception from both critics and audiences.

It is the first series in the Pretty Little Liars franchise, with three spin-offs. The first two, Ravenswood and Pretty Little Liars: The Perfectionists, were both cancelled after one season. An eponymous spinoff premiered on HBO Max in 2022, which focuses on a new cast of characters in a different setting.