This chapter explores the development of Neil Ferguson’s research on political violence from its quantitative social developmentalist roots to his contemporary qualitative research which explores how former and current Northern Irish paramilitaries became involved in, stayed engaged with and eventually began to disengage from politically motived violence as a result of the peace process. The chapter moves on to explore this ‘arc of terrorism’ research in detail and how it underpins Ferguson’s engagement with governmental departments, NGOs, policing and security agencies in order to provide critical advice and guide evidence-based policy and practice in the field of countering violent extremism. The chapter also explores the challenges, problems and pitfalls in the transition from research to practice, exploring both the key weaknesses in the field of terrorism studies more generally, and those faced by the author as he liaised with governmental and non-governmental stakeholders, before concluding with advice for researchers working in this area.