This issue of Thermal Science scientific journal is again dedicated to the research in the field of energy efficiency in transportation sector with special emphasis on thermal processes of internal combustion engines as the main factor in vehicle fuel consumption. According to the opinions of our reviewers (the list of reviewers participating in this issue is given at next page) we have chosen 33 papers for this issue from a large number (about 80) of submitted manuscripts on internal combustion engine and transport energy efficiency problems. Unfortunately, some submitted papers are still under revision and a number of papers have not been accepted for publication because of their lack of scientific level, since they mainly have presented obtained experimental results without any original or new insights. This issue discusses two main problems of current transportation: high pollution caused by toxic engine exhaust emissions and high consumption of fossil fuels. Presented papers suggest that these problems can be solved by further improvement of internal combustion engines, by application of alternative fuels and by introduction of alternative power drive systems. To find optimal solutions for the current world energetic situation, global warming and air pollution, the intensive research in the transportation sector is necessary. Therefore, certain results of these researches are presented in the papers of this issue.