In Transition Science Adviser
Current job: Professor of environmental policy at Harvard University; director of the Science, Technology and Public Policy Program at Harvard's Belfer Center for Science and International Affairs.
Credentials: Holdren, 64, is also director of the Woods Hole Research Institute in Falmouth, Mass. A physicist with degrees from MIT and Stanford, he spent much of his career as a professor at the University of California at Berkeley.
What he offers: Holdren has expertise in two of the thorniest issues facing the Obama White House: energy and climate change.
Quote: "Reliable and affordable energy is essential for meeting basic human needs and fueling economic growth," Holdren told the 2007 meeting of AAAS. "But many of the most difficult and dangerous environmental problems at every level of economic development arise from the harvesting, transport, processing and conversion of energy."