A librarian at Oxford's Bodleian Library has unearthed the earliest-known book dust jacket. Dating from 1830, the jacket wrapped a silk-covered gift book, Friendship's Offering. Silk bindings were very vulnerable to wear and tear, so bookselllers would keep them in these wrappers to protect the binding underneath. When you bought the book you would take the wrapper off and put it on your shelves, which is presumably why so few of these covers have survived.
Unlike today's dust jackets, wrappers of the early 19th century were used to enfold the book completely, like a parcel. Traces of sealing wax where the paper was secured can still be seen on the Bodleian's discovery, along with pointed creases at the edges where the paper had been folded, showing the shape of the book it had enclosed.
The jacket had been separated from its book, and had never been catalogued individually. It remained hidden until the library was contacted by an American scholar of dust jackets looking for the earliest known example.