The Lightning Thief is an American fantasy-adventure novel based on Greek mythology, the first young adult novel written by Rick Riordan in the Percy Jackson & the Olympians series. The manuscript was sold in an auction to Miramax Books, an imprint of Hyperion Books for Children and thus Disney Publishing (succeeded by the Disney Hyperion imprint).

The novel charts the adventures of modern-day twelve-year-old Percy Jackson as he discovers he is a demigod, the son of a mortal woman and the Greek god Poseidon. Percy and his friends Annabeth Chase and Grover Underwood go on a quest to find Zeus's stolen lightning bolt and prevent a war among the gods Zeus, Poseidon, and Hades.

The Lightning Thief was published in July 2005. The book has sold over 1.2 million copies in the subsequent four years, appearing on The New York Times children's Best Seller list and being listed as one of the Young Adult Library Services Association's Best Books for Young Adults, among other awards. It was adapted into a film named Percy Jackson & the Olympians: The Lightning Thief released in the United States on February 12, 2010. This novel is followed by The Sea of Monsters and spawned two sequel series and the extended universe of the Camp Half-Blood chronicles.