Before 9/11, the literature on terrorism and international organizations (IOs) was largely event driven. That is to say, the modest nature of the debate reflected a modest empirical record of IO engagement in responding to terrorism. Moreover, this period saw a correlation between the way states acted against terrorism through IOs and the nature of subsequent debates. Famously, states were (and remain) unable to agree on a definition of “terrorism,” precluding broad-based action through IOs. The findings presented in this literature were furthermore often quite bleak. The immediate post-9/11 period, however, was much more optimistic. This period saw an unprecedented increase in action against terrorism in IOs, primarily through the Security Council resolution 1373. Resolution 1373 elaborates a broad—and mandatory—agenda for counterterrorism cooperation. This resolution has had significant and ongoing consequences for the ways IOs are utilized in the effort to suppress terrorism. Furthermore, this and other IO engagements with terrorism brought about an increase in scholarly interest in the area, even giving rise to a sense of optimism in the literature. Thus, from the pre- to the post-9/11 period, there are elements of both continuity and change in the way scholars have discussed terrorism in the context of IOs.