Defining 'terrorism' has been an issue that has confounded both policymakers and academics. There is little point in expending any further time on what they see as a forlorn exercise, yet for others the lack of progress on an agreed definition leaves a sense of unfulfilled obligation. The chapter outlines some of the reasons why pursuing an agreed 'definition' of terrorism has been seen as so important before summarising the main obstacles that have confronted such an endeavour. It suggests potential avenues that may allow us to view the concept more analytically as a distinctive form of political violence. From an academic perspective, arguments for instilling some sort of analytical quality into 'terrorism' are also compelling. The obstacles to an agreed conceptualisation of terrorism are formidable enough for some to deem the quest a pointless exercise.