All too often, the terms terrorism and insurgency are used interchangeably, just like tactics and strategy. But terrorism is indeed a tactic while insurgency is a strategy, and the two concepts are far from synonymous. This chapter details the differences between terrorism and insurgency, and hence, terrorists and insurgents, by tracing the evolution of each of these terms and placing them in the proper context, while providing numerous examples of terrorist chieftains and insurgent leaders, and how these individuals thought about strategy over time. The chapter will also investigate the considerable overlap between terrorism and insurgency. After all, militants pursuing an insurgent strategy may seek to use terrorism as a tactic toward achieving their objectives. Size can be a useful distinguishing characteristic, because terrorist groups often consist of a small number of individuals. By contrast, insurgent organisations, such as Lebanese Hizballah or the Liberation Tigers of Tamil Eelam (LTTE), number in the thousands. Indeed, many of the most important ‘terrorist’ groups in the world – including Lebanese Hizballah, LTTE, the Provisional Irish Republican Army (PIRA), and the Revolutionary Armed Forces of Colombia (FARC) – are better described as insurgencies that use terrorism than as typical terrorist movements.