Abstract: An adjustable book jacket for covering 100% of the external surface area of book covers in a wide range of book sizes is disclosed. A LYCRA-spandex fabric is cut in a unique diamond shaped pattern which eliminates waste fabric during production, and assures that the differential X and Y axis stretch characteristics of the fabric are properly located on the book jacket. Books of various size are neatly and snugly covered without visible seams, including the external spine portion of the book cover which is secured by the unique spine corner locking mechanism inherent in the combination of the diamond shaped pattern and the two way differential stretch nature of the fabric.