Two decades have now passed since Al-Qaeda militants targeted the United States mainland on 11 September 2001. Since the attacks, the fight against transnational militant Islamism has dominated security agendas in the US, Europe, and beyond, costing the US alone over USD 5.4 trillion and claiming the lives of more than 7,000 US military personnel globally. Despite these costs, the threat from militant Islamism has persisted – and indeed proliferated – since September 2001. At this 20-year mark, Janes Terrorism & Insurgency Centre (JTIC) data offers insights on past trends and future forecasts for transnational militant Islamist activity.