The chapter delves into the development of zero emission engines for commercial aviation through hydrogen fuel cells and electric power trains. The founder and CEO of Zero Avia discusses their progress in creating new generation engines for large aircraft, collaboration with aircraft manufacturers, and plans to have engines for larger aircraft in the next 20 years. The conversation covers the historical context of jet engine development, challenges in transitioning to greener technology, the efficiency of using hydrogen as an energy carrier, and the importance of government and operator support for sustainable aviation.