An economic crisis is an unexpected phenomenon with strong consequences for nations, institutions and people's wealth, habits, and behaviors. It departs from the ‘normal’ evolution of the affairs foreseen by economic theory. It makes the claim for new theoretical explanations. It surprises the economic agents (individuals, firms and governments) that try to ascertain what kind of phenomenon they are facing in order to decide the appropriate actions to undertake. It calls for revisions of theory, plans and expectations. Overall, a crisis calls for an explanation which clarifies its causes.