This issue of the journal Thermal Science continues practice to dedicate a whole issue to the particular topic, or to a prominent scientist. This issue is dedicated to the scientific contribution of Prof. Adrian Bejan, and his influence on many researchers to optimize engineering systems using basic principles of thermodynamics, in particular entropy generation minimization.

Guest editors, Ventsislav Zimparov and Jordan Hristov, did very responsible job in choosing more suitable papers presented at the International Symposium on "Thermal-Fluid Science and Engineering", held in Gabrovo, Bulgaria on 5-6 April 2004.

Ventsislav Zimparov and Jordan Hristov also made first peer review of the papers, and have been in contact with reviewers, and in correspondence with the authors in trying to obtain necessary quality of the papers.

I am very grateful to guest editors Ventsislav Zimparov and Jordan Hristov for their excellent job, and their contribution to the high quality of the journal Thermal Science.

Having in mind the situation in energy sector of the countries in the Balkan region, new Energy policy of European Union formulated in new Green paper, importance of sustainable energy development, and important role of energy efficiency in general energy policy in the future, two new issues of the journal Thermal Science are in preparation - overview of the results of the R&D&D projects financed in the frame of the National Energy Efficiency Program of Serbia, and new issue devoted to the Dubrovnik Conferences on Sustainable Development of Energy, Water and Environment systems held in 2003 and 2005. Those issues will give an insight of the activities in the field of sustainable energy development in countries of the Balkan region.