The dust jacket (sometimes book jacket, dust wrapper or dust cover) of a book is the detachable outer cover, usually made of paper and printed with text and illustrations. This outer cover has folded flaps that hold it to the front and back book covers. Often the back panel or flaps are printed with biographical information about the author, a summary of the book from the publisher (known as a blurb), and/or critical praise from celebrities or authorities in the book's subject area. In addition to its promotional role, the dust jacket protects the book covers from damage. However, since it is itself relatively fragile, and since dust jackets have practical, aesthetic, and sometimes financial value, the jacket may in turn be wrapped in another jacket, usually transparent, especially if the book is a library volume.
Before the 1820s, most books were published as unbound sheets and were generally sold to customers either in this form, or in simple bindings executed for the bookseller, or in bespoke bindings commissioned by the customer. At this date, publishers did not have their books bound in uniform "house" bindings, so there was no reason for them to issue dust jackets. Book owners did occasionally fashion their own jackets out of leather, wallpaper, fur, or other material, and many other types of detachable protective covers were made for codexes, manuscripts, and scrolls from ancient times through the Middle Ages and into the modern period.