The collection of empirical data is essential to an understanding of a phenomenon. However, data collection needs to be guided by theoretical analysis. In this talk I examine two distinct psychological approaches to terrorism that view it as a “syndrome” versus a “tool”. The syndrome perspective assumes that terrorism is a psychologically meaningful entity, i.e. that terrorists are characterized by a specific set of traits that distinguishes them from non terrorists, and that terrorism as a phenomenon has a definite set of root causes (such as poverty, or oppression). The tool perspective (based on goal-systems theory) assumes that terrorism is a means that any social agent (individuals, states, non state agents) could use as a tactic in real or imagined conflict. The employment and the relinquishment of terrorism could be understood in terms of the general dynamics that govern the use of any means toward goal attainment. These two psychological perspectives on terrorism have divergent implications for the kind of data one would collect to further the understanding of this phenomenon, and counteracting it.