Over the last few years, Unmanned Aerial Systems have proved to be highly efficient and capable of performing a wide range of applications, as well as development being more economical when compared to equivalent manned systems. This has resulted in the market for UAS increasing. An emerging role in this market is played by what is referred to as 'HALE' (High Altitude Long Endurance) UAV. This category of UAV presents itself as the ideal platform from which a wide range of different missions can be undertaken, both Military and Civilian, with versatility and a low maintenance cost. As a consequence, a growing number of Aerospace Companies from all over the world have shown interest in this innovative form of UAV. The purpose of this report is to present the design of a contemporary HALE UAV. The design process starts with the Conceptual phase, with the definition of the statistical analysis and the Matching Diagram. The results are optimized in the Preliminary phase by iterative procedures. Tools and methods used to size the aircraft design parameters are also presented. The research for this project was conducted at Imperial College of London and submitted to Politecnico of Turin.