In 2007 the European Union launched the 2020 Climate & Energy Package, with three core targets: A 20 % share of renewable energies, a 20 % cut in greenhouse gas emissions from 1990 levels, and a 20 % increase in energy efficiency. This thesis provides a review of the two legislative pieces that were at the core of the package, the Energy Performance of Buildings Directive of 2010 and the Energy Efficiency Directive of 2012. Buildings account for more than 40 % of the total European energy consumption, making the improvement of building energy performance imperative. The two directives provide a framework for the promotion of energy efficiency by introducing National Energy Efficiency Action Plans, energy efficiency obligation schemes as well as strategies and measures aimed at the improvement of building energy efficiency. Implementation of the directives is examined based on the Austrian legislation concerning energy efficiency and building energy performance. Traditionally legislation on building matters has been the responsibility of the 9 federal states, but in recent years the Austrian Institute of Construction Engineering has promoted harmonization of construction laws through the release of guidelines. Guideline 6 includes provisions implementing core parts of the EPBD, although doubts about the quality and stringency remain. As technological advances and laws on building construction greatly evolved since the 1973 oil crisis the majority of energy performance improvements can be achieved with renovations of the existing building stock, particularly buildings constructed before 1990. A combination of improvements to the building envelope and technical building systems, as well as the increased use of alternative energy sources can reduce the energy demand of buildings by up to 90 % and more. While it is too early to draw conclusions about the effectiveness of regulations that entered into force so recently, financial and administrative barriers and the user-investor-dilemma remain and prevent substantial improvements in the renovation rate of buildings, particularly those privately owned.