Innovation is the engine of change in most industries. But there are some industries where innovation hurts the existing leaders (for example, in the case of digital imaging and Kodak), and there are others where innovation helps the existing leaders (for example, video on demand and Netflix). To help make sense of this puzzle, Clay Christensen developed his theory of innovation. He showed that some innovations have features that make them disruptive, while others have sustaining qualities. It is very useful to understand which is which.