Can great powers reach confident conclusions about the intentions of their peers? Many scholars argue that they can. One set of arguments holds that states can deduce others’ current intentions from certain domestic characteristics such as their foreign policy goals, ideology, or regime type. Another focuses on behavior and maintains that states can infer current intentions by examining their counterparts’ arms policies, membership in international institutions, or past actions in the security realm. A final set of arguments explains why intentions are unlikely to change and thus why current designs are good predictors of future plans. On careful review, these optimistic claims are unpersuasive. Great powers cannot confidently assess the current intentions of others based on the latter's domestic characteristics or behavior, and they are even less sure when it comes to estimating their peers’ future intentions. These findings have important implications for theory and policy. Theoretically, they strengthen structural realism against competing approaches. As for the real world, they suggest that the United States and China are on a collision course if the latter continues to rise and becomes a peer competitor.