This article investigates the use of terror in Colombia's civil war by examining the behavior of the Revolutionary Armed Forces of Colombia (FARC) and the National Liberation Army (ELN). Relying on an extensive database covering 25 years of conflict, the article traces the way in which the FARC and ELN have employed terror as part of their overall insurrectional strategy. I argue that, while ideology plays an important role in inspiring revolutionary terrorism, these groups' terror practices evolved over time and were driven principally by military strategies. Changing conditions in the theater of war, particularly growing competition with paramilitary forces, in turn, influenced these strategies. The article also discusses some interesting differences between the two groups' terror practices.