Sometimes, a major innovation starts at the top of a market and works down—think of Tesla’s electric sports car. Other times, as innovation theorist Clayton Christensen noted in The Innovator’s Dilemma, innovations bubble up from the bottom, beginning with a product that has limited functionality and seems at first like little more than a toy. That second uphill path has been the trajectory of the electric bicycle, which over the past 20 years has become an important mode of personal transportation in China and is now beginning to make inroads in the rest of the world.