The subject of this report is the upending of a floating monopile for an offshore wind turbine foundation. This is an assignment of Van Oord Dredging and Marine Contractors BV. An analytical model has been developed to simulate the upending of a monopile in MapleTM, based on the general theoretical principles and the experience of Van Oord. An experiment was then done to validate the analytical model. The MapleTM script can be used to calculate the forces of the crane for future projects. The monopile, sealed with two end-caps, is towed by a tugboat from the storage site to the installation site and is then upended by the jack-up vessel of Van Oord, the Aeolus. The end-caps guarantee buoyancy during transport and upending. After upending the end-caps are removed, either internally or externally. A conceptual design has been developed for both removal methods. With upending the vertical position of the monopile can be reached with a nett weight of the pile greater than the safe working load of the crane using the buoyant force. The minimum draught needed for the buoyant force to remain within the safe working load of the crane, determines the minimum hydrostatic pressure needed for the external removal of the bottom-cap. The top-cap can only be removed once the pile has been placed on the seabed, since the buoyant force is the auxiliary of the crane. As shown in figure 1, the upending of the monopile is performed, by vertically displacing the connection point between the pile and the crane. Because the crane hook is attached to the pile with a hinge, the monopile can rotate freely around this point. For the analytical model in MapleTM it is assumed that the upending process is quasi-static because the influence of the inertia is negligible. The experiment has confirmed that the inertia may indeed be neglected by showing the similarity between two scaled upending tests at different continuous hoisting velocities and the corresponding quasi-static simulation. Therefore the scaled upending correlates to the quasi-static model. It is found that, only when the lifting starts and stops, and respectively the acceleration and deceleration are relatively large, the inertia influences the upending process. Further research to refine the upending process, as well as the design of the end-caps is recommended. The hoisting speed of the crane can be optimized if the expectations of the experiment and the analytical model are confirmed in practice. The design depends on the airflow when releasing the end-cap and the internal pressure when lowering the pile towards the seabed. The internal pressure can be controlled using a pressure valve. These recommendations will lead to the optimized upending process of monopiles for offshore wind turbine foundations that are transported by towage using end-caps.