This chapter provides a meta-analysis of scientific, empirical research on Environmental Policy Integration (EPI) to address this question. An important finding is the discrepancy between the adoption of EPI in terms of objectives and commitments and its actual implementation, that is, translation into concrete measures. Overall, there are relatively few cases where environmental objectives were given a substantial status in non-environmental policies. The barriers identified suggest that the actual detailed design or architecture of the strategies that are employed to promote EPI really matters.