On May 19, 2011, Amazon announced that in April 2011 its customers purchased more e-books than printed books.  This development occurred less than four years after the debut of Amazon’s e-reader (the Kindle) in November 2007.  Amazon has been selling printed books since July 1995. Source: http://www.forbes.com/sites/ericsavitz/2011/05/19/amazon-says-now-selling-more-e-books-than-print-books/