Dear colleagues, readers of the journal Thermal Science Journal Thermal Science is trying already 10 years to inform you about recent achievements in thermal sciences, mostly fundamental ones. We are, normally more oriented to the results achieved in South East European Region, but, also, many contributions presented recent results obtained in developed and other countries in the world. From the beginning, our orientation was not only to pay attention to the fundamental research, but also to reveal mutual influence of investigations and practice, i.e. mutual influence of the modern technology development and goal oriented fundamental and applied research. Also, we tried to put together investigation oriented to the mechanical engineering (mostly energy production and consumption), chemical and process engineering and ecology. We have tried to be forum for mutual discussions between researchers from the South East European region. Such intentions can be easily seen, especially in our special issues. No. 2, 2004 was devoted to the fundamental research of biomass transformations in energy production units, due to the increased interest for biomass use, as renewable energy source. No.3, 2005, a special issue devoted to the Dubrovnik Conference on Sustainable development, make possible to join authors from many countries from South East European region, to discuss about presently most prominent topic ? sustainable development. Papers gave an insight in the research and engineering activities in the countries of the region in the field of sustainable energy development. Proceeding with policy to point out connections between fundamental research and practice, special issue devoted to prof. Adrian Bejan, was prepared (No.1, 2006). Following up this line, to insist on mutual influence of fundamental research and practice, and to inform about activities in the South East European Region, mainly oriented to the sustainable energy development, energy efficiency and renewable energy sources and ecology, new special issue devoted to the R&D results obtained in the frame of the National Energy Efficiency Program of the Serbian Ministry of science and environmental protection, is planned as No. 4, 2006. As an introduction to this issue, in present number of the Thermal Science review paper ENERGY EFFCIENCY IN SERBIA, Research and development activity is included. Also, No.3, 2006 follow the same line, and will be devoted to the 2005 International Symposium "Moving Towards Zero Emission Plants", held in Greece, and will present mainly activity in Greece in mentioned field. For the next year, special issue (No.2, 2007) will present most interesting papers from Dubrovnik Conferences held in 2003 and 2005. We are sure, that such publishing policy will contribute to make stronger influence of technology development to the choice of research topics in thermal sciences in the countries of the south East European Region. Our intention is to present also in more details activities in sustainable development, energy efficiency, use of renewable energy sources in other countries of the region. 4 july 2006 Prof. dr. Simeon Oka Editor-in-chief