This essay is brief and artless. It is also slightly derivative from my own earlier work. Twenty years ago, I wrote an essay on terrorism, against the background of the troubles in Northern Ireland, but reaching back to the long tradition of revolutionary violence, which was what explained the essay’s reference to Red and White terror (Ryan 1991). On this occasion, the background of recent terrorist attacks on the United States, Spain, and Britain is too obtrusive to be ignored; and the continued violence in Iraq, which may (or may not) have diminished by the time this volume appears in the bookstores, is also too obtrusive and too much to the purpose of this essay to be ignored. Many of the earlier essay’s assumptions about the aims and methods of contemporary terrorism were based on the activities of the IRA and ETA, and have become irrelevant to present purposes; its view of how terrorism should be understood, however, is something on which I have not changed my mind. So, the first part of this essay contains some reflections on risk, and the second the direct and particular relevance of those reflections to the topic of terrorism.