The dust jacket (sometimes dust wrapper or dust cover) of a book is the outer cover, which is often detachable and often illustrated. This outer cover has folded front and back flaps, by which it attaches to the front and back book covers themselves. Often the front flap summarises the contents of the book, provides biographical information about the author and offers words of praise (known as a blurb) from celebrities or authorities in the book's subject area on the back flap.
Dust jackets serve to protect the book covers from damage. However, they are themselves relatively fragile, and since dust jackets have intrinsic, aesthetic and financial value, the jacket may in turn be wrapped in transparent acetate. In the world of book collecting the presence or absence of an original dust jacket can have a significant impact on a collectible book's value.
In schools, teachers often require students to use a removable "book cover" to protect textbooks. Made of paper, fabric, or plastic, these function like a dust jacket to protect the front and back cover from damage.