With a view to improving energy efficiency of buildings in the European Union the Energy Performance of Buildings Directive was adopted, according to which the ‘nearly zero-energy building’ means a building that has a very high energy performance. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources. This thesis explores the definition of nearly zero-energy buildings, framework for the calculation of energy performance of buildings and characteristics of nearly zero-energy buildings in accordance with the Energy Performance of Buildings Directive in order to reduce energy consumption and reliance on energy from non-renewable sources. Nearly zero-energy buildings described in this thesis are connected to the grid, while the definition of such buildings is based on the balance between the energy taken from the grid and the energy supplied to the grid in a certain period. Photovoltaic systems, solar collectors, ground source heat pumps, biomass stoves, district heating and air conditioning are just some of the technologies and renewable energy sources that ensure nearly zero energy consumption. In addition to obtaining energy from renewable sources that partially cover the necessary amount for the operation of the building, it is necessary to implement measures to increase energy efficiency that affect energy consumption in buildings, and measures relating to the building envelope (insulation, thermal mass, windows, reflective roofs), the internal conditions and the installation of the building (electric lighting, heating, ventilation and air conditioning). A comparison of buildings across the EU members has shown that there is a noticeable difference in ambition when it comes to setting up the definition of nearly zero-energy buildings. The results obtained show that energy efficiency measures in the building envelope are not sufficient to achieve nearly zero energy consumption, and that it is necessary to increase the share of energy from renewable sources in order to achieve the set goal. The goal of nearly zero-energy buildings is to achieve a high level of thermal comfort, reducing overall energy consumption and greenhouse gas emissions, increasing the efficiency of lighting, heating, cooling, ventilation and electrical installation. According to the Directive, all new public buildings must be nearly zero-energy buildings by the end of 2018, and all new buildings must be nearly zero-energy buildings by the end of 2020 [1].