11 Birthdays is a children's time loop novel written by Wendy Mass and published in 2009 by Scholastic Press.

The novel follows the life of a young girl named Amanda Ellerby who has spent each of her first ten birthdays with the same boy, her best friend Leonard "Leo" Fitzpatrick.

The Bulletin of the Center for Children's Books published a review by Jeannette Hulick, which states that 11 Birthdays “is imaginatively developed and kid-pleasing.

The now-tenuous/now-tenacious quality of the book’s middle-grade friendships will ring true to its audience, and Amanda’s voice is likable and humorous.”[2] Publishers Weekly also states, “Like a Groundhog Day for middle grade readers, Mass' winning story features a girl seemingly trapped in her 11th birthday.

They also all revolve around birthdays and are set in the same small town of Willow Falls, with the presence of the mysterious Angelina D’Angelo.