Fascinating stuff:

During the 2008–2012 period, trade sales overall rose a total of 14.2%, with the increase due entirely to the introduction of e-books. During the period, sales of print trade books fell 8.4%, from $13.1 billion to just over $12 billion in 2012. The BookStats figures document the important role adult fiction has played in the growth of e-books. In 2012, e-book sales in the segment rose 42%, to $1.8 billion, while sales of adult nonfiction increased 22%. Within the trade category, children’s/young adult had the strongest gain, with sales jumping 117%, from $215.9 million to $469.2 million.

via BEA 2013: The E-book Boom Years.