This thesis examines and compares Swedish and Norwegian energy intensive industry firms’ lobbying during the revision of the European Emissions Trading Scheme. In the applied framework of lobbying routes two key explanatory factors receive attention. First, the origin from the EU member state Sweden or non-member Norway; and secondly, the size of the company. Six companies are chosen as cases: Norsk Hydro ASA, Norcem AS and Norske Skog from Norway; and SSAB AB, Cementa AB and Svenska Cellulosa Aktiebolaget from Sweden. Qualitative interviews with company representatives provide the data used to test hypotheses on firms’ lobbying routes. A key finding is the extensive use of European associations by all firms to lobby the European Parliament, the European Commission and the Council of the European Union. Similarly, the use of national associations seems to be prevalent, pointing at benefits in better institutional response to collective lobbying and resource-sharing aspects. Norwegian firms, however, seem to struggle more than Swedish firms regarding lobbying the European Union institutions due to inferior access into the EU when lobbying directly, through national associations or national institutions. Not all the differences among the companies can be explained by originating from a EU member state Sweden or non-member Norway. While company size affects the number of available lobbying routes positively, this appears to be also dependent on cross-border production and possibly also on other influences. The results attempt to challenge some assumptions made in earlier literature and to contribute some new knowledge to a field that has not yet received extensive attention.