Humanitarians are no longer necessarily viewed as selfless angels in war zones. Their motivations and mastery, their principles and products are questioned from inside and outside of the community of aid and protection agencies. Like the poor, war victims will always be with us. Coming to their rescue requires understanding of the ongoing transformations to contemporary humanitarian action in wars and the evolution of humanitarian culture – its values, language and behavior. An agreed culture of cooperation has given way to a contested one of competition resulting from militarization, politicization and marketization. Preventing mass atrocities is preferable to halting them; but the record of preventing them has been dismal. And even with sufficient political will to act or react, the history of postintervention results also has been abysmal. When mass atrocity prevention fails, a ‘learning culture’ is required: more responsible reflection and less rapid reaction. Traditional principles are unhelpful; guidance to effective action does not require strict adherence to humanitarian ideology but rather to considered calculations about least worst options.