On April 15, 2013, two bombs exploded near the finish line of the 117th annual running of the Boston Marathon, killing three people outright and wounding more than 260 so severely they had to be hospitalized - many losing limbs or suffering other permanent injuries. This “no notice” event was extremely challenging for emergency responders and law enforcement, as they coped with the evacuation of the wounded and tens of thousands of bystanders, launched a massive criminal investigation to identify the perpetrators, and five days later captured them in a dramatic 20-hour police action. This talk will describe the events of that week, analyze aspects of the emergency response that went well and badly, and consider what lessons might be drawn for others who have to plan security for major athletic events like world - class marathons, the Olympics, or the World Cup.