In late 2006, heavily armed Ethiopian troops invaded Somalia with tacit support of the United States. Subsequently, Ethiopia used two legal justifications for its military intervention, namely, an inherent right of self-defense and an invitation from the transitional government of Somalia. If nothing else, it appears Ethiopia and the United States wanted to seek a casus belli for military intervention against Union of Islamic Courts. This article examines whether the Ethiopian intervention can be justified as an exception to the general prohibition of the use of force embodied in the United Nations Charter.