The construction industry is a large contributor to CO2 emissions, with buildings responsible for 40% of the total European energy consumption and a third of CO2 emissions. Therefore the construction sector plays a significant role fulfilling the 20/20 targets of the European Union - Reduction of the energy and the CO2 emissions by 20% and increase of the total energy share with renewable energy sources to 20%. In order to understand, address and finally reduce the environmental emissions, the method of Life Cycle Assessment (LCA) plays a key role. In recent years LCAs of buildings and building products become increasingly important. Unfortunately with the number of applications inconsistencies increased as well. The "Energy-efficient Buildings Initiative" (EeB-PPP) and the European Union funded the research project "Operational Guidance for performing Life Cycle Assessment Studies of the Energy efficient building Initiative (EeBGuide)" to harmonize these approaches and to provide LCA practitioners guidance on specific LCA questions. Furthermore the EeBGuide supports building certification and EPD schemes with environmental aspects. These guidelines and instructions will form the basis for consistent and transparent high quality LCAs and therefore serve as a step leading to low environmental impact buildings and building products and to a sustainable future.