Do international reputations matter and are they transferable from one context to another? These critically important questions continue to frame policy debates surrounding US responses to crises in Syria and Ukraine. For skeptics, past actions and reputations for resolve have no bearing on an adversary's assessment of US credibility; relative “power” and “interests” explain behaviour (Hopf, 1994; Mercer, 1996; Press, 2005; Walt, 2013; Zakaria 2013). We argue that scholars who dismiss the relevance of reputations typically sidestep important questions about how adversaries actually acquire relevant information about US interests and power. Building on an extensive collection of qualitative and quantitative studies of US deterrence encounters in asymmetric conflicts over the last two decades, we argue that lessons from past actions inform an adversary's interpretation of US interests in any given case and provide crucial information about Washington's willingness to deploy military force (capabilities). By implication, lessons learned from Bosnia 1992–1995 informed actions in Kosovo 1999, which, in turn, informed subsequent assessments of US interests and commitments in Iraq 1991, 1998 and 2003. Similarly, lessons about US reputations and credibility in Iraq from 1991 to 2003 were critically important to successful WMD diplomacy in Syria. Policy implications are addressed in the conclusion.