Abstract: A book jacket with flaps folding over the front and rear covers of a book, having informative indicia located on the inner surface of the flaps such that when the flaps are folded out, the informative indicia will be juxtaposed with the book and will be concurrently visible to the user as he views the pages of the book. The informative indicia provide information to help the user of the book interpret the information in the book. For example, the informative indicia may be: a family tree for a book involving a complex genealogy, a timeline of events for a book on history, or a legend of map symbols for an atlas or road map book. The informative indicia may be printed directly on the inner surface of the flap, or may be provided on a separate sheet which is attached to the inner surface of the flap. If there is a great deal of information to be provided, an elongated folded flap may be employed.