Automatic flight control systems are of paramount importance in AWE applications. State estimation, control algorithms and avionics must ensure robust and accurate tracking of power-optimal orbits by a wind energy kite in varying wind conditions. A second critical challenge for these complex systems is the autonomous launching and landing of the flying vehicle. This report presents the work that has been carried out by ESR14 at the Automatic Control laboratory at EPFL over three years to design, implement and validate a flight control system for rigid-wing AWE kites. It will be shown that nonlinear model predictive control methods provide a unifying framework for controlling both soft- and rigid-wing kites in different operational modes. By combining advanced numerical methods with an efficient implementation, it has become possible to apply the approach for real-time flight control of a small-scale prototype.