Book excerpt: Available online: https://pub.norden.org/temanord2021-539/ The Nordic economies are strongly integrated but have chosen different pathways and climate policy instruments to reduce their climate impact. Therefore, the Nordic economic actors have different incentives, even though they operate in the same integrated markets. This can lead to negative spill-over effects on neighbouring countries.This report presents examples of such negative effects within transportation, waste management, energy production. Following an analysis of these, the report identifies a series of barriers for the countries to avoiding the counterproductive, spill-over effects. The report concludes by summing up recommendations for possible improvements the Nordic collaboration.The report has been prepared by COWI. It has included a desk study, stakeholder interviews and two cross-Nordic workshops to verify the findings and identify Nordic challenges and opportunities