This paper uses the eruption of the Icelandic volcano Eyjafjallaj?kull in April and May 2010 as a case study of disruption to civil aviation by airborne ash, with emphasis on risk management aspects. Severe curtailment of flights over much of Europe took place during the crisis, which lasted for slightly more than one week. More than 8.5 million passengers were stranded and commerce was profoundly affected. The United Kingdom was one of the worst impacted countries and took the lead in managing the crisis. The paper considers elements of the decision-making process that formed the basis of the UK Government’s emergency response. It examines the relations between science, governance, and economi c imperatives. Physical thresholds guiding decisions to restrict airspace were defined somewhat arbitrarily, which may have increased disruption. A damaging form of risk aversion prevailed at certain points in the crisis. Lack of preexisting procedures and planning meant that the response to dynamically changing meteorological conditions had to be improvised. At the same time, lack of integration between different modes in the European transportation system meant that had the crisis continued any longer there would have been severe problems in moving stranded people and commodities, as well as soaring economic losses. Eruptions similar to or more serious than that of Eyjafjallaj?kull are perfectly possible in Europe in the not-too-distant future.