Humanitarian intervention is a use of military force to address extraordinary suffering of people, such as genocide or similar, large-scale violation of basic of human rights, where people’s suffering results from their own government’s actions or failures to act. These interventions are also called “armed interventions,” or “armed humanitarian interventions,” or “humanitarian wars. They are interventions to protect, defend, or rescue other people from gross abuse attributable to their own government. The armed intervention is conducted without the consent of the offending nation. Those intervening militarily are one or more states, or international organizations. The need to consider and understand the many issues involved in humanitarian interventions have been borne home by the fact that these interventions has become more complex and more common since the 1980s, and because of the consequences of non-intervention, such as in the Rwandan genocide of 1994, in which nearly one million people were killed in less than three months. Humanitarian interventions raise many complex, inter-related issues of international law, international relations, political philosophy, and ethics. This article considers moral issues of whether or when humanitarian intervention is justified, using just war theory as a framework. Section One addresses general characterizations of humanitarian interventions and commonly discussed cases, as well as some definitional or terminological issues. Section Two examines the question: What humanitarian emergencies rise to a level at which intervention is appropriate? Section Three presents just war theory as a common framework for justifying humanitarian interventions. Section Four considers some other, related issues that may support or challenge armed interventions: international law, state sovereignty, the selectivity problem, political realism, post-colonialist and feminist critiques, and pacifism.