Agile methods in general have arise from a mixture of sound practice and good principles, but they lack an over all theory. Complexity Science, coupled with insights from the Cognitive Sciences challenges the basic assumptions of systems thinking and idealist uses of "self-organisation" alike. This presentation will provide an overview of CAS, and more specifically the Cynefin framework which has been widely adopted within the AGILE Community. It will examine the critical role that constraints play in allowing evolution to take place in systems and the implications for team formation, requirements capture and project monitoring. Fundamentally it will challenge a purely engineering approach to systems involving human agency. It will focus on effectiveness, not efficiency and resilience not robustness.