“The department of engineers, who design, improve and manage energy systems in the most efficient and sustainable way” Energy is in the center of almost everything in the nature, in society and indeed in the universe. Energy systems engineering is a multidisciplinary approach of improving all energy systems, from manufacturing to end using. Limited energy sources, energy efficiency/saving and management, renewable energy (solar, biomass, hydraulic, wind, geothermal etc.), the issues about the raising energy producing and usage are presenting the need of experts, that have studied in the energy system engineering branch, increasingly. In this context, the energy sector is undergoing a big change with the pressure of environmental restrictions (like the combustion related contaminants and greenhouse gas emissions), the increment of the fuel prices, the decreasing of the fossil fuels and the decreasing control on the energy market. Energy systems engineers are in the center of such issues.