Justine Larbalestier is an Australian young adult author. She is best known for the Magic or Madness trilogy: Magic or Madness, Magic Lessons and the newly released Magic's Child. She also wrote one adult non-fiction book, the Hugo-nominated The Battle of the Sexes in Science Fiction (Best Related Book, 2003), and edited another, Daughters of Earth: Feminist Science Fiction in the Twentieth Century.

Larbalestier was born and raised in Sydney, Australia. She now alternates living between Sydney and New York City.

In 2001, Justine married fellow author Scott Westerfeld.