The diffusion of applied knowledge, both within and between countries, is one of the sources of economic growth. The spread of such knowledge is also necessary to deal with climate change. Yet economists and environmentalists alike know little about the process. This useful book -- a thorough piece of practical research -- looks closely at how clean energy technologies such as gas turbines, advanced batteries, solar photovoltaics, and coal gasification emerged and spread to China. Gallagher bases her case studies not only on data and written material but also on nearly a hundred interviews she conducted with participants in the clean energy sector. She finds many of the usual problems faced by cross-border businesses. But her book also suggests some reasons for optimism. Much diffusion of technology does occur, both through direct investment and through licensing. Intellectual property issues, although present, rarely prove insuperable. China is developing new indigenous technology and even exporting it. China’s patent system is growing rapidly, and Chinese courts are gradually developing the capacity to resolve patent disputes impartially.