The book claims that Leonardo Da Vinci is one of the Grand Masters of the organization called Priory of Sion that protects the bloodline of Jesus and Mary Magdalene. His involvement on the book was more of his famous paintings which the author has shown much ignorance in his interpretation of Leonardo Da Vinci's work of art such as the Mona Lisa, Madonna on the Rocks and the Last Supper. \n\nThe book is just a fiction. And it has no evidences to support its claims. \n\nTo understand more about Leonardo Da Vinci and how he was associated in the book, allow me to refer you to this site: http://www.jesusdecoded.com/leonardo1.php?page=100