Dear readers, This is the first time that Thermal Science journal publish special issue devoted to energy efficiency in buildings - topic not in first focus of the journal. The main reason why we accepted proposal to publish special issue with selected papers presented at the 1st International Conference on Buildings, Energy, Systems and Technology (BEST 2016), is that for solving the problems in energy systems in buildings we need synergetic engagement of experts with different skills: mechanical engineers, civil engineers, architectures, electro engineers, and experts in urban planning, energy planning, energy strategy makers, and many others. For Thermal Science journal is of special interest that processes that have to be investigates to enhance energy efficiency in buildings are in essence - fluid-flow, heat and mass transfer, combustion and other chemical processes, using tools, theoretical and experimental, that are developed in fluid mechanics and thermodynamics, including mathematical modelling and CFD. To publish papers dealing with synergy of investigations in different sciences and technology development of equipment and systems, is one of most important goals of Editorial Board of the Thermal Science journal. We believe that this special issue will present that such synergy is inevitable if we wish to achieve sustainable and efficient use of energy in buildings. In the name of National Editorial Board of the Thermal Science journal, and in our own name, we are grateful to Prof. Vincenzo Corrado, Guest Editor, for his great efforts to invite respectable reviewers, and for his excellent selection of papers. Grace to respectable scientific experience of Prof. Vincenzo Corrado, and his wide insight in state-of-the-art in the field of energy efficiency in buildings, we obtained not only insight in research achievements oriented to enhance energy efficiency in buildings in South East European Region, but also, looking at his Editorial, we could compare those achievements and worlds trends, and especially to compare them with trends in European Union. National Editorial Board is also especially thankful to Prof. Milica Popović-Jovanović, Faculty of Architecture, University of Belgrade, Belgrade, who initiated publishing of this special issue, for her permanent engagement to stimulate authors to submit papers and to find financial support for this special issue. (October 31st, 2018, Belgrade)