This report compiles major results of the 4-year DLR Project Wetter & Fliegen. Contributing DLR institutes and facilities were the Institutes of Atmospheric Physics, Flight Systems, Flight Guidance, Robotics and Mechatronics, Aerodynamics and Flow Technology, Air Transportation Systems as well as DLR Flight Experiments and Systemhaus Technik. The aim was to contribute to safety and efficiency of tomorrow’s air transportation by a) developing weather and wake vortex expert systems along with operational concepts for the air traffic management and control at airports and b) researching new sensors and delivering automated flight control and innovative flight crew information technologies for the aircraft. Deeper insights were gained into wake vortex physics, the consequences for wake-encountering aircraft and separation prediction, as well as the detection, tracking and prediction of adverse weather phenomena like thunderstorms and snow and icing conditions. New operational concepts for air traffic control and tools for flight systems have been developed and the expert systems have been assessed from a technological and economical perspective. Prototype systems have been matured towards different levels of technology readiness and have been tested and evaluated with human-in-the-loop simulations and in field campaigns in real environments. Building on these achievements the work will be continued in the forthcoming DLR Project Weather Optimised Air Traffic.