Political institutions play a significant role in the logic of environmental sustainability, in particular for the contribution they can make to the ambitious goals of the Paris Agreement for a global action plan aimed at limiting global warming to well below 2°C. Municipal governments can develop specific actions and initiatives that can considerably foster a local sustainable development, where the dialogue and cooperation between political and socio-economic actors become a key element. For municipalities, an effective way for supporting the Local Agenda 21 projects and environmental performance improvement is derived from the introduction of a systemic approach for environmental management. By implementing an environmental management system (EMS), municipalities not only can improve the management effectiveness and efficiency, but they can also meet their legal obligations specifically related to the development of local environmental policies and action plans, and improve the transparency to the public about the natural environment quality and environmental protection initiatives. The integration of an Energy Management System (EnMS) can strengthen the actions for a continuous improvement of energy efficiency and, consequently, the attainment of specific energy saving targets in line with the national energy saving targets. The focus of the present paper is aimed at defining the possible actions needed to integrate an EnMS into an implemented and certified EMS. The results of a step-by-step analysis carried out by taking into account the case study of the Municipality of Udine are here presented.