Despite uncertainty, people are born to act. Faced with environmental aggression and upheaval, inaction is more stressful than action. What choices, strategies or methods need to be implemented so that action is as effective as possible in terms of the objectives to be achieved? We should not delude ourselves about the term "good decision", which does not have much meaning when we act in an uncertain environment and when we know the weakness of forecasts. However, we must know how to act and be capable of taking the most appropriate action. Action in Uncertainty is a real guide to taking effective action when nothing is certain. According to the different types of uncertainty, what are the respective good uses of expertise and intuition? How do we motivate teams and avoid cognitive bias and manipulation? These themes are dealt with in clear and accessible terms to help decision-makers make the right choices in a world that is more uncertain than ever.