Half a decade into the e-book revolution, though, the prognosis for traditional books is suddenly looking brighter. Hardcover books are displaying surprising resiliency. The growth in e-book sales is slowing markedly. And purchases of e-readers are actually shrinking, as consumers opt instead for multipurpose tablets. It may be that e-books, rather than replacing printed books, will ultimately serve a role more like that of audio books—a complement to traditional reading, not a substitute.