This chapter outlines the nature of the Improvised Explosive Device (IED) threat and the various points at which innovation can and does occur within the IED system. It examines innovation in relation to the IED through the lens of a counter-terrorism practitioner. The chapter explores some of the generic factors that influence IED design, fabrication and emplacement. It draws on the work of O'Sullivan and Dooley. The chapter argues that extremist groupings usually innovate in order to keep the security forces off-balance and to remain unpredictable. It concurs with the work of Jackson, in that extremists do not tend to innovate for the sake of innovating'. It also provides a predictive methodology in order to identify where the extremist may go next or what his trajectory might be, particularly if one is aware of the future intentions of the security forces in terms of Techniques and Procedures (TTPs) and technology.