This chapter aims to explore some of the key debates and arguments surrounding the concept of terrorism. Terrorism has long featured as an integral part of the international security environment but has taken special prominence as such since 9/11. This chapter will ﬁrst consider the concept of terrorism, starting with the perennial issue of deﬁnitions and how the concept has changed, and culminating in a brief examination of the nature and threat posed by Al Qaeda. Having established the main contours of the terrorist threat, the remainder of the chapter will deal with some of the potential responses utilized by the international community. This chapter will focus on two types of international response to terrorism. First, the so-called soft-line response that aims to identify and then rectify the alleged root causes of terrorism. Second, the contribution that the Armed Forces can make in combating terrorism will be examined.