Joshua Geltzer is a fellow in New America's International Security program. He served from 2015 to 2017 as senior director for counterterrorism at the National Security Council staff, having served previously as deputy legal advisor to the National Security Council and as counsel to the assistant attorney general for national security at the Department of Justice. He also served as a law clerk to Justice Stephen Breyer of the U.S. Supreme Court and, before that, as a law clerk to Chief Judge Alex Kozinski of the Ninth Circuit Court of Appeals. Josh received his J.D. from Yale Law School, where he served as editor-in-chief of the Yale Law Journal, and his PhD in War Studies from King’s College London, where he was a Marshall Scholar. Before that, he attended Princeton University, majoring in the Woodrow Wilson School of Public and International Affairs. He is the author of US Counter-Terrorism Strategy and al-Qaeda: Signalling and the Terrorist World-View, published by Routledge; and his work has appeared in Parameters, Studies in Conflict & Terrorism, the Journal of Constitutional Law, and the Berkeley Journal of International Law.