The terrorist attacks of September 11, 2001, have had tragic effects for history teachers and students in Canada, the United States, and abroad. Yet, despite increased educational research in historical thinking, very little is known about students' historical understanding of terrorism. This exploratory study looks at some Canadian, but specifically Ontario, high school students' abilities to think historically when analyzing current events such as the terrorist attacks of September 11. Drawing on recent discussions among educators and historians, it generates four competencies for historical thinking (sense of empathy, awareness of continuity and change, appreciation of evidence, and sense of historical meaning-making). These competencies are then used as a framework for an empirical investigation with two classes of grade 10 history students. The findings suggest that Canadian students are not only emotionally affected by the aftermath of September 11, but also have developed more or less sophisticated historical understandings of terrorism.