In 2012, US President Barack Obama stated that Syrian government usage of chemical weapons on its population would cross a red line that would require the US government to reconsider its approach to the civil war then underway in Syria. Syria subsequently used such weapons, creating a policy dilemma for the United States about how to respond to Syrian President Bashar al-Assad's violation of the red line. In Coercing Syria on Chemical Weapons, Matthew Moran, Wyn Q. Bowen, and Jeffrey W. Knopf examine efforts by the United States, sometimes acting with France and the United Kingdom, to respond to Syria's possession and use of chemical weapons over the course of its civil war. In particular, they focus on US strategy, covering the presidencies of both Barack Obama and Donald Trump, which relied heavily on coercion involving both deterrent and compellent variants of that strategy. As the authors show, policies directed at the ruling Assad regime in Syria attempted to deter chemical weapons attacks and to compel Syria into giving up its chemical arsenal with mixed outcomes. Drawing on existing literature on deterrence and coercive diplomacy to identify three propositions—involving credibility, motivations, and assurances—the book explains the mixed record of coercive success and failure and examines how effective coercive strategies were at different points and why. Deriving lessons from the most significant attempt in the post-Cold War era to deter use of a weapon of mass destruction, this book offers theoretical and practical lessons for both security studies scholars and policymakers.