Theme of the final thesis is importance of energy certificate in society. Adjustment Croatian legislation with european acquis communautaire is described detailed in introduction of this thesis. Energy certificate in accordance with current legislative framework give us information about consumption energy used for heating, and proposed measures for improvement energy performance of all energetic systems. Energy performance of buildings is calculated or measured amount of energy required to meet energy needs during typical use of the building witch among other includes energy used for heating, cooling, ventilation, preparation of hot water and illumination. Algorithm for calculating the energy performace of buildings is described in detail in metodology, which can be found on internet website of the Ministry of construction an physical planning (www.mgipu.hr). Thesis describes metodology of implementation: energy audit of buildings, purpose of the energy audit, implementation steps of the energy audit, preparation of the energy audit, how to perform existing condition overview of the building, example of proposed measures for energy efficiency improvement and example for energy certificate.