Terrorism (from the Latin verb terrere : to frighten) is neither a 21st century nor a 20th century phenomenon. It did not begin with Al Qaeda nor even with the IRA. The term was first used in 1794 during the French Revolution and referred to a supporter of the Jacobins. If we use the term liberally, the term can be used at least as far back as the 1st century CE with the assassination of Roman sympathisers in Judea by the Sicarii Zealots. In this lecture, we will trace the development of terrorism through Guy Fawkes, Irish republicanism, the Baader-Meinhof gang and the Italian left-wing terrorism in the 1970s. We will consider the rise of the PLO, Al Qaeda and 'Daesh', asking the fundamental question, why do people behave in such ways? Who is attacked and what is the politics of selection? Why were young women targeted in the recent Manchester attack? Can we explain such behaviour with sociological or psychosocial models, or, in the 21st century, is a neurobiological account more insightful? Is the terrorist psychopathic? Or mentally ill? Or neither? Can we talk about the terrorist psychology in the singular or is better to talk about terrorist psychologies? What about victims of terrorism? What sorts of mental scars are left on survivors and how are mental health problems dealt with? To conclude, we will consider post-traumatic stress in survivors of Lockerbie and 9/11. This topic can be highly charged and we will deal with questions such as those above in a sensitive but direct manner.