Both threats and assurances can be useful in international negotiations. Threats help convince the adversary that a state will fight if challenged, and assurances can convince the adversary that a state will not attack if not challenged. We develop a model that analyzes when threats and assurances are used. Threats are widely useful because there is typically a range of outcomes that are preferable to war for each side, and threats can secure a better deal within that range by strengthening a state’s bottom line. In contrast, assurances are only necessary when war would result without them because of insufficiently valued intermediate outcomes or shifting power. We discuss insights from the model, including the role of false assurances, in the context of both the Sudetenland crisis and Cold War Europe.