The concept of organizational improvisation is gaining interest to understand how it is possible to act in real time in a context of uncertainty and of time pressure. Current research studies raise the question of organizational memory : face to new situations, it is to capitalize knowledge and to explore solutions in real time. How can an organization leverage this knowledge repository to improvise effectively ? During improvisational situations, how can it be strengthened ? To answer these questions, this article draws on the results of the longitudinal case study of two NGOs that face a humanitarian emergency.