Marc Sageman, a forensic psychiatrist and former intelligence officer, is the author of seminal, though not uncontroversial, works like Understanding Terror Networks (2004) and Leaderless Jihad (2008). [His last book, Misunderstanding Terrorism (2016) was reviewed in this journal in the February 2017 issue.] In his latest book, he looks at two hundred years of mainly European political violence in an effort to explain radicalisation to terrorism, including what he terms ‘neojihadi’ campaigns against the West.