In many ways, EPI constitutes one of the guiding axioms of green thinking and practice. Therefore, whether or not policy systems faithfully put it into practice is a matter of enormous importance to not only students of green politics but also policy practitioners too. Its aims are certainly nothing less than radical – to turn the policy status quo on its head, such that environmental protection involves a much more holistic and, above all, proactive search early on in the policy process for opportunities to prevent environmental damage from occurring. However, academic research on EPI only really began to take off in the late 1990s. In this article we have sought to review the state of the art and identify key trends in both academic thinking and policy practice.