This thesis provides a good introduction to the American environmental certification system LEED, Leadership in Energy and Environmental Design, and trough compar-isons between Sweden and the United States an explanation to the systems design is given. The work is closely linked to a LEED Core & Shell project in Stockholm, Swe-den, where the goal is to reach the second highest rating in LEED - Gold. This thesis gives a broad description of the LEED system and a more profound study of the energy sector, Energy and Atmosphere. Here, for example, an analysis has been made of how the energy consumption of an imaginary building designed according to the requirements of the BBR (Swedish building code) performs in comparison to the Baseline building in LEED. The existing model of Borgarfjord 3, which served as a case study in this work, has al-so been modified to investigate the energy savings that could have been achieved by adding extra insulation to the building. A description of the problems, regarding how the Swedish district heating system (DES) is treated in LEED, is given as well as the suggested modifications. This is an issue that will be pursued during the process of shaping a new, international, version of LEED due to be launched 2012.