In the 1970s, the notion of social "complexity" appeared simultaneously in the realms of policy research and domestic policy, as well as in theories of international relations and foreign policy. The concept proliferated quickly, reaching its culmination around the middle of the decade before quietly disappearing by the late 1970s. It is this short boom of appearance and disappearance which may shed light on the discontinuities and peculiarities of the 1970s. This project aims to explain why the notion of social complexity appeared and flourished at that particular time and in those two realms, and how these realms were related to one another. Its main hypothesis attributes the discovery of social complexity in the 1970s to a historical moment when reality seemed so elusive as to defy contemporary observersí established categories and theories, exceeding their intellectual grasp and resisting political intervention. This is what sets the 1970s apart from preceding decades. New assumptions and policies were needed to catch up with a world that had profoundly changed. Project duration: June 2012 to September 2014.