Thermal systems, which refer to several distinct thermodynamic quantities, are relevant in many industrial problems and environmental phenomena. Among others one can mention Energy production industries such as renewable energy productions, waste energy recovery systems and internal combustion engines. While analysing any of these, one can readably recognize the influence of such energy system on the environment due their inter-exchangeable energy transfer/work load. As can be seen, many aspects of our social/engineering problems are inter-connected through a thermal system. Therefore, this Special Issue (SI), named “Energy and Environment”, focused on various aspects of fluid dynamic, thermodynamic and heat transfer researches that have emphasis on the contributions of the fundamental thermal aspects of energy and environment systems and their application in engineering problems. This research topic welcomed novel inter-/multi-disciplinary works in the emerging area of energy, mechanical, electrical, material, chemical, civil, aerospace and nano-engineering. Manuscripts dealing with the implementation and development of a special technology for one of the above-mentioned engineering disciplines that are transferable to others also fall within the scope of this special issue. Papers ranging from new physical models and discoveries to the correct treatment of difficulties inherent to modelling and simulation of related systems were considered. These included but were not limited to: Thermal Aspects of Energy and Environmental Engineering Thermal Aspects of Renewable Energies (Solar, Wind, Biomass, Geothermal, Wave, etc.) Thermal Aspects of Energy and Environmental Engineering in Micro and Nano Dimensions Transport Processes (mass, energy, charge, momentum and angular momentum) New Methods of Measuring and/or Correlating Transport-Property Data Thermal Aspects of Multi-Physical Effects Energy Efficiency in Conventional Energy Production Units (combustion process, gas turbines, bubbly reactors, etc.) as well as Alternative Energy Technologies “Energy and Environment” call was initially opened on 1 March 2019 to invite original ground-breaking articles in the field. The closing date for the call was 15 October 2019 where 42 submissions were accepted for publication in the Journal of Thermal Analysis and Calorimetry which is the leading journal in the field. It is noted that we also invited ten selected articles out of more than 200 submitted articles to the 2nd National Conference on Internal Combustion Engine, held in Babol Nooshirvani University of Technology, Babol, Iran. Finally, we would like to thank all authors who contributed suitable papers to the special. We also would like to thank all of the reviewers who had provided their critical comments. A special thanks to the Journal Editor-in-Chief, Professor Szilágyi, for giving us this opportunity to edit this Special Issue.