Book 1,3,4,5 are Hardcover, book number 2 is a softcover.

The Heroes of Olympus Hardcover Set by Rick Riordan is a collection of 4 hardcover books and 1 softcover book in the set, published by Disney Publishing Worldwide in 2014. This boxed set includes a total of 2404 pages and features illustrations by the author himself. The series falls under the genres of juvenile fiction, with themes of legends, myths, fantasy, magic, and action and adventure. The books are written in English and cater to readers interested in Greek and Roman mythology within a fantasy setting.