From The Art and Popular Culture Encyclopedia
The term book cover applies to a range of protective coverings that are used to bind together the pages of a book. Beyond the familiar distinction between hardcovers and paperbacks, there are further alternatives and additions, such as dust jackets, ring-binding, and out-dated forms such as the nineteenth-century "paper-boards" and the even more antiquated hand-binding.
Before the early nineteenth century, books were hand-bound, in the case of luxury medieval manuscripts using materials such as gold, silver and jewels. For hundreds of years, book bindings had functioned as a protective device for the expensively printed or hand-made pages, and as a decorative tribute to their cultural authority. In the 1820s great changes began to occur in how a book might be covered, with the gradual introduction of techniques for mechanical book-binding. Cloth, and then paper, became the staple materials used when books became so cheap—thanks to the introduction of steam-powered presses and mechanically-produced paper—that to have them hand-bound became disproportionate to the cost of the book itself.
Not only were the new types of book-covers cheaper to produce, they were also printable, using multi-colour lithography, and later, half-tone illustration processes. Techniques borrowed from the nineteenth-century poster-artists gradually infiltrated the book industry, as did the professional practice of graphic design. The book cover became more than just a protection for the pages, taking on the function of advertising, and communicating information about the text inside.