(Hattem 2015). His assessment was condemned from across the political spectrum, from critics on both the left (including then Democratic presidential candidate Hillary Clinton) and right (including then GOP presidential candidate Rick Santorum). Similar public debates erupted following other violent incidents, including the bombing at the Boston Marathon and shooting in Orlando, Florida. These debates highlight not only the contentiousness of classifying terrorism, but also the stakes involved in doing so, for policy makers, academics, and members of the public alike. In this article, we turn to experimental methods to explain the tenor of these public debates. We investigate terrorism in a public opinion context not because we believe that the mass public's intuitions can necessarily resolve normative debates about what should or should not be considered terrorism, but rather because of the central role that public opinion plays in our understanding of how terrorism works. In a vast array of prior research, terrorism is understood as a form of violence that functions by attracting public attention. It is because terrorism hinges on public reaction that Margaret Thatcher suggested terrorists depend on "the oxygen of publicity," that Carlo Pisacane declared terrorism to be "propaganda by deed," and that Ayman al-Zawahiri suggested that for al-Qaeda, media coverage is "more than half" the battle (Smith and Walsh 2013, 312). If the responses of ordinary citizens constitute a central causal mechanism through which terrorism operates, it logically follows that understanding what ordinary citizens think terrorism is is a crucial prerequisite to understanding how they react to it.