Spencer Jill Hastings is a fictional character, one of the five main characters who appear in the Pretty Little Liars novel series and its Freeform television adaptation. Created by American author Sara Shepard, she is a member of the group known as the Liars, and is best friend to the four other members, who are protagonists of the story. Portrayed by Troian Bellisario, the character was developed for television by the series' showrunner I. Marlene King and appeared in each of the show's 160 episodes during its seven-years-long run, from its premiere on June 8, 2010, to its finale on June 27, 2017.

Spencer is known in the fictional town of Rosewood for her sophisticated charm, intelligence, hardheadedness, and, at times, dangerous dedication to achieve her life goals. She is part of the very wealthy, powerful Hastings family; Spencer's parents, Veronica and Peter, are both linked to politics and her sister, Melissa is an almost-equally accomplished grad student.

For her role as Spencer, Bellisario was nominated thrice for Choice Summer TV Star: Female (winning once) and twice for Choice TV Actress: Drama (winning once) in the Teen Choice Awards.

Spencer is one of four primary protagonists in all sixteen of the Pretty Little Liars novels, starting with 2006's Pretty Little Liars. She is portrayed as a competitive girl who strives for perfection in everything she does. Spencer is willing to do whatever it takes to win, often to the detriment of herself and others. She is known to have a dark side and suffers from rage-induced black outs, which leads her to question whether she had anything to do with the death of her friend Alison. She also exhibits symptoms of OCD but it is never confirmed whether she has the disorder.

In later books, Spencer is briefly addicted to drugs, which she takes to help her improve her grades at a University of Pennsylvania summer school. It is also revealed that her father had an affair with Jessica DiLaurentis around the time of Spencer's conception, making her the half-sister of Alison and Courtney DiLaurentis.

Spencer has an ongoing rivalry with her older sister, Melissa, who is equally competitive. The two slowly come to an understanding and eventually have an improved relationship.

Troian Bellisario was cast as Spencer Hastings for the Pretty Little Liars television series adaptation in November 2009.

Spencer is similar to her book counterpart: she is portrayed as a highly ambitious, intelligent young woman from a wealthy family who frequently competes with her older sister Melissa for accolades and the approval of their parents. However, in the show, Spencer is portrayed as more emotional and sentimental, and more humorous than her book counterpart. She's the most academically gifted of her friends, and in the running for valedictorian. Spencer is on the Rosewood Day field hockey team, and plays tennis at her family's country club. She was the only one who could ever stand up to Alison, although she still deferred to Alison.