Marc Sageman, M.D., Ph.D., is a former CIA Operations Officer (covered as a Foreign Service officer) who was based in Islamabad from 1987 to 1989, where he worked closely with Afghanistan's mujahedin. He has advised various branches of the U.S. government in the War on Terror. He is also a forensic psychiatrist and a counter-terrorism consultant.
He first drew wide attention for his book Understanding Terror Networks, a book that The Economist called "influential." "The most sophisticated analysis of global jihadis yet published. . . . His conclusions have demolished much of the conventional wisdom about who joins jihadi groups."
In Leaderless Jihad: Terror Networks in the Twenty-First Century, Sageman "suggests that radicalization is a collective rather than an individual process in which friendship and kinship are key components." After the book was negatively reviewed by Bruce Hoffman in Foreign Affairs, a debate, which was covered by The New York Times, ensued between him and Sageman. In this debate, Sageman argue that terrorism is now "bottom up" where terrorist act as lone wolf or radicalized person create terrorist structure.
In The London Bombings, Sageman investigates four bombing plots from an intelligence viewpoint: Operation Crevice (in relation to the fertiliser bomb plot), Operation Theseus (which investigated the July 7 2005 attacks), Operation Vivace (which investigated the failed July 21 2005 plot) and Operation Overt (in relation to the liquid bomb airline plot). Reviewed by Dr Anthony Richards, Royal Holloway College in 'Perspectives on Terrorism' 
- Understanding Terror Networks (Philadelphia: University of Pennsylvania Press, 2004)
- Leaderless Jihad: Terror Networks in the Twenty-First Century (Philadelphia: University of Pennsylvania Press, 2008)
- Misunderstanding Terrorism (Philadelphia: University of Pennsylvania Press, 2016)
- The London Bombings (Philadelphia: University of Pennsylvania Press, 2019)
- Bunch of Guys, counter-terrorism term referring to self-organizing terrorist cells
- Operation Cyclone
- "Understanding Terror Networks". University of Pennsylvania Press.
- "How jihad went freelance". The Economist. 2008-01-31.
- William Dalrymple, New York Review of Books
- Hoffman, Bruce. "The Myth of Grass-Roots Terrorism". Foreign Affairs. Retrieved 2009-03-19.
- "Does Osama Still Call the Shots?". Foreign Affairs. Retrieved 2009-03-19.
- Sciolino, Elaine; Schmitt, Eric (June 8, 2008). "A Not Very Private Feud Over Terrorism". The New York Times. Retrieved 2009-03-19.