Donald Macrae, Risk and Regulation Advisory Council UK illustrates that the ash cloud incident involved many risk actors and, by relying on the methodology developed by the UK’s Risk and Regulation Advisory Council to manage “Public Risk” incidents, offers an insightful analysis of the different role that these actors played in the unfolding of the event. 1st HEC workshop on regulation. Emergency regulation under the thread of a catastrophe: a hard look at the volcanic ash crisis. A conference organised by Alberto Alemanno, HEC Paris. 10 & 11 november 2010. More info at http://www.albertoalemanno.eu