Introduction: As societies and their governments seek tools to help foresee and evaluate the future impacts of their current choices, successful policy foresight can benefit from learning from hindsight – from retrospective studies of the accuracy and impact of RIA and EIA (and other IA systems) on past decisions, both to revise current policies and also to improve the accuracy of IA systems in the future. This chapter discusses the ongoing diffusion of IA, and the pros and cons of combining the array of existing IA systems into a new and better system of Integrated Impact Assessment (IIA) (both prospective and retrospective) encompassing the full portfolio of important impacts
