This book presents a curated collection of works addressing topics on aerodynamic and structural design of aerospace systems, with a particular emphasis on technologies that enhance the design process. A set of case studies illustrate how Digital Twins are used in supporting analyses and design of complex systems. Works developed within research environments, academia and industries contributes to provide an overview on the status of Digital Twins technology for aerospace applications. Examples in which the adoption of Reduced Order Models (ROM) support the generation of models that provide real time feedback on performance are provided. Aspects related to the accuracy of numerical models, and the efficiency of optimisation techniques, are also covered.