Kevin Bullis, in this issue's cover story ("Sun + Water = Fuel"), reports on work by MIT's Daniel Nocera and others to unlock the potential of solar energy through artificial photosynthesis. "Solar power only works when the sun's out. If it's ever going to oust fossil fuels, we'll need a way to store the energy from sunlight cheaply, so we can use it after the sun sets," Bullis says. "Now chemists, by imitating the way plants store energy from the sun, may have found a way to do this, clearing the way for solar power that works day and night. The advance has ignited intense interest and controversy--making it a fascinating area to report on." Bullis is Technology Review's energy editor.

Graham Allison wrote this issue's essay on the prospect of nuclear terrorism ("Nuclear Deterrence in the Age of Nuclear Terrorism"). "By a combination of good sense, great fortune, and grace, we survived and protected both peace and freedom during the Cold War--without a nuclear Armageddon," says ­Allison. "The 21st century poses new threats that will require new thinking about unthinkables." This essay extends the argument in his 2004 book, Nuclear Terrorism: The Ultimate Preventable Catastrophe, which was selected by the New York Times as one of the "100 most notable books of the year." Allison served as assistant secretary of defense in the first Clinton administration; he currently directs the Belfer Center for Science and International Affairs at Harvard's Kennedy School of Government, where he also teaches.