John Paul Holdren (born March 1, 1944) is an American scientist renowned for his work in environmental science, physics, energy policy, and climate change. He served as Assistant to the President for Science and Technology, Director of the White House Office of Science and Technology Policy (OSTP), and Co-Chair of the President's Council of Advisors on Science and Technology (PCAST) during Barack Obama's administration from 2009 to 2017. In these roles, he advised on critical issues including global environmental change, energy transitions, nuclear arms control, and international scientific cooperation. Prior to his government service, he was a prominent academic, holding positions including Teresa and John Heinz Professor of Environmental Policy at Harvard University's John F. Kennedy School of Government (now professor emeritus), Professor of Environmental Science and Public Policy in Harvard's Department of Earth and Planetary Sciences, and Director of the Woods Hole Research Center (now Woodwell Climate Research Center) from 2005 to 2008. He also served on the faculty at the University of California, Berkeley, from 1973 to 1996, where he co-founded the Energy and Resources Group. Holdren's research focuses on the causes and consequences of global environmental change, energy options for industrial and developing countries, and international security. He has authored or co-authored over 300 articles and papers, as well as numerous books including 'Energy' (1971), 'EcoScience' (1977), and 'Ending the Energy Stalemate' (2004). His contributions have earned him prestigious honors such as membership in the National Academy of Sciences, National Academy of Engineering, and American Academy of Arts and Sciences; a MacArthur Fellowship (1981); the Tyler Prize for Environmental Achievement (2000); and the 2026 AIP Karl Compton Medal. Holdren has also held leadership roles including President of the American Association for the Advancement of Science (2006-2007) and Chair of the National Academy of Sciences Committee on International Security and Arms Control (1994-2005). He served as a science advisor to President Bill Clinton and was involved in the bipartisan National Commission on Energy Policy. Now retired from his Harvard professorships as of June 2021, Holdren continues as Research Professor and Co-Director of the Science, Technology, and Public Policy Program at Harvard's Kennedy School, President Emeritus and Senior Advisor at the Woodwell Climate Research Center, and Visiting Distinguished Professor at Tsinghua University in Beijing.