According to the Sherman Anti-Trust Act: "A market share greater than 75 percent indicates monopoly power, a share less than 50 percent does not, and shares bet

According to the Sherman Anti-Trust Act: "A market share greater than 75 percent indicates monopoly power, a share less than 50 percent does not, and shares between 50 and 75 percent are inconclusive in and of themselves." http://legal-dictionary.thefreedictionary.com/Sherman+Anti-Trust+Act http://legal-dictionary.thefreedictionary.com/Sherman+Anti-T... So by this standard, they are an ebook monopoly, but not necessarily one that would be slapped by the feds, provided that people believe Amazon's large market share wasn't the result of abused or unfair power.