The financial crisis of 2007–8 was experienced and reflected upon as a crisis of knowledge, the perennial question being why nobody accurately understood the risks that were being taken within the financial sector. In the wake of the crisis, there have been demands that rational economic knowledge be extended further and more vigorously, to prevent such ignorance being possible in future. At the same time, there have been demands for a new, softer rationalism, which factors in the possibility of errors and systemic complexities. What neither approach recognizes is that ignorance is not simply the absence of rational economic knowledge, but is a productive force in itself, something that is actively nurtured and exploited, both by neo-liberal theorists such as Hayek and by expert actors who have been implicated in the financial crisis. We explore how ignorance has been alternately an albatross, a commodity and an institutional alibi to financial actors and the scholars who study them.