By early September in 1999, many feared genocide in East Timor was imminent. Following a UN-sanctioned referendum, in which the East Timorese people voted in favour of independence rather than autonomy within Indonesia, violence had exploded in the province. Militias, intimately linked with the Indonesian armed forces, were perpetrating massacres, destroying infrastructure and forcibly displacing tens of thousands of East Timorese. Jailed independence leader Xanana Gusmao warned: ‘We foresee chaos. We foresee … genocide in East Timor’, a view shared by many experts on the region. Yet these dire predictions did not come to pass. Australia declared its willingness to lead an international peacekeeping force and, under overwhelming international pressure, Indonesia acquiesced to the intervention. Within days of UN-authorisation, the first troops of INTERFET arrived in Dili, and the risk of genocide very quickly abated. This chapter examines the factors that led up to this crucial intervention and enabled a timely and robust international response to the crisis. It concludes by considering how lessons from this example can inform an evidence-based approach to genocide prevention.