The "Tomorrow Series" is a popular young adult book series written by Australian author John Marsden. It follows a group of teenagers who band together to survive after their country is invaded by an unknown military force. The story is told from the perspective of Ellie Linton, one of the main characters, as she navigates the challenges of war, friendship, and personal growth. The series consists of seven books, starting with "Tomorrow, When the War Began." It explores themes of resilience, courage, and the impact of conflict on youth. The books have been well-received and have also been adapted into a film and a television series, further expanding their reach and influence.