International organizations have carried out hundreds of crisis management operations aimed at ending violence. Yet one strategic error in an operation can have deadly consequences. Scholars have widely examined organizational learning without examining the pre-condition for learning: institutional memory. This talk will explain how international organizations acquire memory from their failures at a time of increased turnover. It argues that organization elites use informal processes facilitated by the secretariat to socially construct institutional memory of strategic errors. Informal processes include transnational interpersonal networks, private documentation and scenario-based exercises. Surprisingly, existing formal processes - such as lessons learned offices and databases - prove ineffective at retaining relevant knowledge. The talk adopts a mixed-method approach to test the argument in NATO. Methodologies include structured interviews with 120 NATO elites, a survey experiment in the field and case studies of crisis management in Afghanistan, Libya and Ukraine.