Global warming and reduction of CO2 emission are hot topics locally, nationally and globally these years. The majority of the international society has recognized the necessity of targeting our use of nature resources in order to fight environmental hazards. Sustainable energy is one of the paths leading towards the goal.

This thesis analyses, how sustainable energy has been increasingly implemented in Danish municipalities throughout the past four decades, exemplified by two case studies. The two chosen case studies, the municipalities of Aero and Albertslund, are both so-called ‘green municipalities’ and good, sustainable examples of how reduction of CO2 emission has been put on the agenda in highly different ways, among other things depending of geography.

The data used is publicly available material by the chosen municipalities and other governmental authorities plus a qualitative interview with a leading energy official at the municipality of Aero.

Based on Geels’ MLP theory and Liebowitz and Margolis’ theory of path dependence, with a supplementary from Coenen et al., and Unruh’s theory about lock-in, the thesis analyses how and why Denmark historically has been locked in a production and/or usage of fossil fuel – and how the pattern is broken.

The conclusion of the thesis is that the pattern is slowly breaking, however, strongly depending on geographic conditions and technological development.

The increased implementation is highly due to factors such as increased focus on climate changes, limited access/high price levels on fossil fuel, political pressure locally, nationally and globally, and a high degree of lobbyism from environmental interest groups.