U.S. presidents can choose the form of international agreements that they negotiate. Using the Constitution's Article II procedure to gain ratification of a formal treaty is a costly and time-consuming endeavor, so presidents frequently turn to executive agreements that do not require approval by two thirds of the Senate. Given this alternative, why do presidents ever choose the Article II procedure? This article argues that treaties serve as a costly signal of intent to comply with the terms of international agreements. The choice between treaties and executive agreements is therefore a strategic executive decision that takes into account the anticipated reactions of other states. A signaling model predicts that high-benefit agreements should take the form of treaties. The predictions of purely domestic models of a positive relationship between the reliability of a government and the probability that an agreement is a treaty should not hold. These propositions are tested on a large data set of U.S. international agreements between 1980 and 1999.