Energy technology innovation has played central role in the evolution and advancement of the energy sector. The major challenges facing the energy system-ensuring adequacy supply of energy services at low cost while mitigating adverse local and global environmental impacts-will doubtless require further innovation (i.e., research, development, demonstration and deployment) in energy technologies. Yet our understanding of the global energy innovation system is incomplete, with a majority of analyses focusing on energy research and development in industrialized countries, and within that domain, on funding levels. A much more systematic effort is warranted to assess, and fill, the gaps in understanding of the global energy innovation system-only then we will able to develop appropriate policies to guide this system to enable it to meet future challenges.