The 30th International Conference on Efficiency, Cost, Optimization, and Environmental Impact of Energy Systems (ECOS) http://www.ecosconference.org was held from June 2 through 6, 2017 at San Diego State University’s Conrad Prebys Aztec Student Union Building. The conference gathered over 270 attendees from all over the world. Cutting-edge research papers were presented at the conference by many of the leading international researchers on several subjects related to energy. The conference chair of this anniversary conference was our own Prof. Asfaw Beyene. VP of SDSU’s vice president for research and dean of the Graduate Division as well as Dean of College of Engineering, Prof. Monte Mehrabadi and Mechanical Engineering Department Chair Prof. John Abraham attended the opening ceremony. Some faculty from SDSU and from our department presented their research papers and also chaired some sessions. The Conference was very successful. The gala dinner of June 5, 2016 was a climax, Prof. Beyene said. The conference was sponsored by SDSU’s Sustainable Energy Center, Solar Turbine, Energies Publishing company, and Sempra energy.