■The commitment of participants to a project especially under extreme conditions, such as a polar expedition, has a vital bearing on its end result. But how can one apprehend the very notion of commitment? First, we distinguish the actors' "declared" motivations from what actually mobilizes them in the situation. Second, we use notions of mobilization, norms, and sensibilities in order to understand this phenomenon. They throw a light on the participants' behavior throughout the polar expedition and the project's progress. Our conclusions lead to a reconsideration of how to recruit for project teams, highlighting as they do, on the one hand, the importance of commitment not just in terms on intensity but also of meaning, and on the other, the difficulty of using this criterion for recruiting insofar as this commitment may be separate from the motivation expressed.