The notion that we live in publishing’s digital age faces a new challenge. Earlier this year, we learned that print may be getting a second wind. This week, the latest sales numbers from leading publishers show a decline in e-books.

"The big question is, What is up with e-books?--or I should say, down with e-books? In their financial results posted this week, lower e-book sales were a big factor in weak financial performances at HarperCollins, and in limiting the gains at an otherwise good quarter for Simon & Schuster. Hachette also reported underwhelming numbers," says Andrew Albanese, Publishers Weekly senior writer.

Of course, the digital revolution has not actually retreated--ask anyone with a smartphone. Yet industry executives say they are “watching closely” as e-book sales and total digital revenues disappoint. What do they see as behind the shift?

"In Frankfurt, the discussions I had with the major publishers revealed largely that no one seemed to expect this dip to last. Although, I have to say, no one could explain what was happening," Albanese tells CCC's Chris Kenneally. "Print, while up in some sectors, is not picking up the slack for the loss in e-books. And I, for one, am concerned that lost e-book sales, means lost readers."