This IDS Bulletin is the second of two that follow an Institute of Development Studies event seeking to define an agenda for research and practice of development impact evaluation. It focuses on exploring the potential of systems ideas and complexity concepts to meet the increasingly complex challenges of an increasingly ambitious development agenda. In particular, the contributions seek to: (a) redefine ‘learning’ according to the number of ‘learning loops’ involved; (b) understand how to identify the most relevant impact evaluation questions; (c) simulate systems states in two sectors (leather and health) following the implementation of (combinations of) different policy options and other events; and finally, (d) shake the foundations of the impact evaluation institutional system, recommending that the notions of multiple perspectives and system boundaries are fully embraced, and that the system ultimately transitions from an ‘evaluation industrial complex’ to an ‘evaluation adaptive complex’. While the issue is a step in the right direction, much more work remains to be done.