God books are books held in place of a shield. A player first receives a damaged book and needs to add 4 torn pages to make a complete god book: Saradomin's Holy Book, Guthix's book of balance, or Zamorak's unholy book. Once a book is filled with 4 pages, you can gain access to 3 more god books.
These books are a quite effective offhand weapon, with slight offensive and/or defensive bonuses, and a great prayer bonus (+5) aswell.
You can buy damaged books from the Lighthouse, north of Barbarian Agility course. An Agility level of 35 is required to pass the rocks to lighthouse (if you don't have the required level, you can run southwest from the Oracle's rock crabs teleport). After the release of Treasure Trails, God pages were released, providing the ability to make the god books using a damaged book from the Lighthouse.