Insider reflections on the political and ethical ‘red lines’ that shape talks with armed interlocutors, be they states or insurgents. After many years in the little-known world of back-channel mediation, helping sworn adversaries to prevent, manage or resolve conflict, Pierre Hazan felt compelled to re-examine the acute practical and ethical dilemmas that affected his work in Bosnia, Ukraine, the Sahel and the Central African Republic. What is the mediator’s responsibility when two belligerents conclude a peace agreement to the detriment of a third? Should mediators never be party to ‘ethnic cleansing’, even if it saves lives? Is a fragile peace worth sacrificing justice for—or will that sacrifice fuel another cycle of violence?In an increasingly dystopian world, Negotiating with the Devil offers both practical guidelines and a moral compass for mediators whose field of action has transformed dramatically. We have gone from soft to hard power; from ‘peace dividends’ to war in Europe; from the end of one Cold War to a new East–West confrontation in Ukraine; from Pax Americana to a multipolar world; from the dream of an all-powerful UN to the organisation’s marginalisation. Against this tapestry, Hazan sheds light on the complex work of those steering peace negotiations, blending vivid first-hand observation with sharp insights into the psychology of compromise as a first step towards peace.