The rise of the e-book in the US and UK
In Britain more than £24m was spent on printed books in the last week of March 2011, but that is a 12% drop compared with the same week last year, and it was the 10th week this year that sales have fallen.
E-book devices can carry more than 1,000 titles at any one time.
Penguin chief executive, John Makinson, explains how sales of paperbacks are affected.