The Leviathan Book was a collection of facts and instructions for the Leviathan people. Those in the cult commonly referred to it as simply "the book." The book traveled from 1797 to 1969 with Barnabas Collins inside the Naga Box (887, 889, 892).
When he fell under the influence of the Leviathans, David Collins was the only one who could read the book (896). It detailed the history of the Leviathans, explaining what had occurred in the past and what needed to happen to ensure the future of the race. The book outlined specific plans for the wedding of the Leviathan leader to a human being (936).
The rules of the book included instructions not to kill. The Leviathans used other methods to deal with their enemies (918).