In its full-year report for 2012, the Association of American Publishers reported that 22.55% of US book sales last year came from e-books. That share was dramatic rise from the 17% that ebooks grabbed in 2011 and 3% in 2009. Overall revenues were up 6.2% to 7.1 billion in 2012. And so e-books are now a $1.54 billion business.