Renewable energy is gaining currency around the globe, but China and the United States are central to its development. They are the world's top-two countries in terms of energy consumption, net oil imports, and carbon emissions, as well as gross domestic product (GDP) and manufacturing. Their large territories harbor some of the best sites to generate renewable energy. If the United States and China cooperate-and compete-effectively, renewable energy can contribute to economic growth, energy security, and climate change mitigation. The past two years saw important developments, including a...