Threats of armed force are frequently employed in international affairs, yet they have received little ethical scrutiny in their own right. This article addresses that deficit by examining how threats, taken as a speech act, require a moral assessment that is distinctive vis-à-vis the actual use of armed force. This is done first by classifying threats within the framework of speech act theory. Then, applying standard just war criteria, we analyze conditional threats of harm under Thomas Schelling's twofold distinction of compellence and deterrence. We aim to show how threats of armed attack, while subject to many of the same evaluative principles as the corresponding use of force, nevertheless have distinctive characteristics of their own. These are outlined under the headings of just cause, ad bellum proportionality, legitimate authority, and right intention. The overall aim is to explain how threats in the international sphere represent a special category that warrants a just war analysis.