This article examines the legal nature of the principles of impartiality and neutrality of humanitarian action, focusing on States as humanitarian actors. It argues that international law does not provide a general legal basis for the universal applicability of these principles, contrary to a common interpretation of the International Court of Justice's 1986 judgment in the Nicaragua case. Nevertheless, impartiality and neutrality may have a significant legal effect on the conduct of States. They may be directly binding on States through the operation of Security Council resolutions drafted in mandatory language. In addition, they may have indirect effect due to the States' obligation to respect humanitarian organizations' adherence to the principles. On the basis of this argument, the article pleads for increased conceptual clarity and, in turn, effectiveness of humanitarian action.