Abstract: This chapter reviews the evolution of Martha Crenshaw’s interests in and approaches to researching terrorism, a trajectory that begins in the 1960s and extends to the present. The story is necessarily partial and incomplete as well as personal. Her first research project concentrated on the use of terrorism by the FLN during the Algerian War, and her current research deals with patterns of cooperation and competition among militant groups and with the relationship between jihadist-oriented transnational terrorism and civil war. Along the way she has analyzed the causes of terrorism as well as its endings, individual motivations for terrorism, group strategies, organizational dynamics, political contexts for terrorism, state responses, and the consequences of counterterrorist policies. Terrorism remains a challenging topic for research as well as a persistent policy problem for decision-makers. We still struggle to explain both the “why” and the “how” of terrorism.