This open access book presents technologies and methods of lightweight system design to support future low-emission aviation in achieving climate targets. It will be shown how reduction of weight and aerodynamic drag affects the energy consumption of commercial aircraft and what characterizes lightweight system design. Methods, design principles, production technologies and options for functional integration are available for more energy-efficient aircraft. Research results from the last decade are presented, which are intended to encourage the reader to further research and, above all, to implement them in future aircraft.