Fangirl is a young adult novel by Rainbow Rowell, published in 2013. Fangirl is Rowell's second published young adult book, following Eleanor & Park, and third published book overall.

Twin sisters Cath and Wren begin their freshman year at the University of Nebraska–Lincoln. While the more outgoing Wren is making new friends and partying, Cath struggles to adjust due to her social anxiety. Most of Cath's free time is spent writing fan fiction (mostly slash fiction) about the fictional Simon Snow series; though the sisters once enjoyed fan fiction together, Wren professes to have outgrown it and distances herself from Cath.

Cath becomes more interested in her writing classes and befriends her classmate Nick, whom she regularly meets for writing sessions. Despite this, she remains depressed; her roommate Reagan and Reagan's friend Levi decide to try and help her. As Cath becomes closer to Levi, he eventually reveals he is romantically interested in her. Just before finals, Cath's father has a bipolar episode, and is involuntarily committed to a psychiatric hospital. Cath ditches her exams and her final paper to take care of her father.

Cath nearly gives up on her studies, Wren, and her friends, but ultimately decides to continue and learn how to cope with her problems. Cath and her sister reunite in the hospital after Wren gets alcohol poisoning. Cath encounters her mother there, who had abandoned them years before. As the school year ends, Cath finishes her novel, and struggles to write an original short story for her class.

Rowell stated that most of the characters have names taken from buildings on the University of Nebraska–Lincoln's campus.

Cather "Cath" Avery

Wren Avery

Levi Stewart