"Percy Jackson & The Olympians" is a popular book series written by Rick Riordan. It follows the adventures of a young boy named Percy Jackson, who discovers he is a demigod, the son of Poseidon, the Greek god of the sea. The series combines elements of Greek mythology with modern-day settings, as Percy and his friends embark on quests to prevent disasters among the gods. The story begins with Percy attending a summer camp called Camp Half-Blood, where demigods train and learn about their heritage. Throughout the series, Percy faces various challenges, battles mythical creatures, and uncovers secrets about his past, all while navigating the complexities of friendship and heroism.