This thesis will describe and analyse how three local companies, that are all subsidiaries to the municipality in Gothenburg City, justify their work with environmental lobbying towards the European Union. These three companies are: Johanneberg Science Park, Gothenburg Energy and Business Region Gothenburg. This thesis will apply Rational Choice Institutionalism and Logic of Appropriateness in order to find how these companies justify their work with environmental lobbyism towards the EU. The thesis will analyse data gathered through expert interviews with strategically selected employees from these companies who have many years of expertise in their respective area. In addition to the interviews, reports from the projects they have participated in, as well as annual reports and documents will be analysed by doing a content analysis. The findings of this thesis are that these companies seem to justify their participation and lobbying practices in line with the two theories. However, the companies seem to justify the participation in line with Rational Choice Institutionalism more often than in line with the Logic of Appropriateness. On the other hand, the analysis show that what seem to be rational according to the companies do not have to rule out that it can be appropriate at the same time.