As a result of the attacks against the United States on September 11, 2001 then President George W Bush declared a war on terror. Six days later, Bush signed a directive which authorized the Central Intelligence Agency to carry out targeted killings against predefined individuals with the purpose to prevent any future attacks from the terrorist network Al Qaeda, as well as the Taliban and associated forces. In conjunction with the declaration of war president Bush initiated the American practice of so-called "drone strikes" with the intention to eliminate suspected terrorists without access to a fair trial, the practice has continued under the mandate of the Obama-administration. The aim of this study is to examine whether the US legal justification for the use of targeted killings and unmanned aerial vehicles in the war against terrorism can be regarded as compatible with the doctrine of just war theory and applicable international law. Furthermore, the study examines the effects of the US practice on international humanitarian customary law in relation to the civilian population. The U.S. justification of targeted killing is compared with international law to determine the lawfulness from a legal perspective. Furthermore, the study demonstrates that the practice is not compatible with the doctrine of just war theory and applicable international law. The use of drones violates international customary law in relation to how they are used under the current conflict.