"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 various threats to both the mortal and divine worlds. Throughout the series, Percy attends Camp Half-Blood, a summer camp for demigods, where he learns about his heritage and trains for battles against mythological creatures. The story explores themes of friendship, bravery, and identity, making it appealing to readers of all ages.