It is believed to be the world’s most valuable book but you may never have heard of it. And now it’s up for auction with an estimated sale price of between $15-$30 million. We tell you what the extremely rare and pricey tome is when we get a firsthand look at it in our studio on Tuesday. Joining us are David Redden, Director of Special Projects and Worldwide Chairman of Sotheby’s Books Department, the auction house in New York where the book will be offered up for sale later this year; and David Spadafora, President of Chicago's Newberry Library where the very rare book will be on display on Wednesday, Sept. 11 from 10:00 am to 4:00 pm. Learn more about the book and the auction here.