Frequent compliance with the adjudicative decisions of international institutions, such as the International Court of Justice (ICJ), is puzzling because these institutions do not have the power domestic courts possess to impose sanctions. This Article uses game theory to explain the power of international adjudication via a set of expressive theories, showing how law can be effective without sanctions. When two parties disagree about conventions that arise in recurrent situations involving coordination, such as a convention of deferring to territorial claims of first possessors, the pronouncements of third-party legal decision makers-adjudicators--can influence their behavior in two ways. First, adjudicative expression may construct focal points that clarify ambiguities in the convention. Second, adjudicative expression may provide signals that cause parties to update their beliefs about the facts that determine how the convention applies. Even without the power of sanctions or legitimacy, an adjudicator's focal points and signals influence the parties' behavior. After explaining the expressive power of adjudication, this Article applies the analysis to a range of third-party efforts to resolve international disputes, including a comprehensive review of the docket of the International Court of Justice. We find strong empirical support for the theory that adjudication works by clarifying ambiguous conventions or facts via cheap talk or signaling. We claim that the theory has broad implications for understanding the power of adjudication generally.