Agenda setting is a crucial aspect of the public policy process. Sudden, rare, and harmful events, known as focusing events, can be important influences on the policy process. Such events can reveal current and potential future harms, mobilize people and groups to address the policy failures that may be revealed by such events, and open the “window of opportunity” for intensive policy discussion and potential policy change. But focusing events operate differently at different times and in different policy domains. Although the idea of focusing events is firmly rooted in Kingdon’s “streams approach” to the policy process, focusing events are an important element of most contemporary theories of the policy process. But not every event works as a focusing event. The process by which a focusing event can yield policy change is complex and involves attention to the problems revealed by the event as well as evidence of learning from the event on the part of policymakers. Although focusing events are important, in many ways the concept remains underdeveloped, with few researchers seeking to understand the dynamics of these important events.