The motivation for the AVATAR project lies in the fact that upscaling wind turbine designs towards 10-20 MW requires radical innovations to make this feasible. Many of these innovationshave a strong aerodynamic component and can be considered as unconventional from an aerodynamic point of view. As such the analysis of the resulting rotor designs falls outside the validated range of applicability of the current state of the art computational aerodynamic tools.The overall objective of the AVATAR project is then to evaluate, validate and improve aerodynamic and aero-elastic tools to ensure applicability for large wind turbines. The capability of these models to produce valid load calculations at all modeling complexity levels needs to be demonstrated. This leads to a number of secondary objectives related to the assessment and evaluation of such designs eventually culminating in new design guidelines.In the AVATAR workplan aerodynamic models are developed and calibrated for all aspects which play a role in the design of large wind turbines. Thereto the entire chain of aerodynamic modelling is mobilized ranging from computational efficient engineering tools to very advanced high fidelity but computationally expensive tools. The development of new comprehensive models is based on a philosophy in which the high fidelity tools feed results towards the lower complexity tools where furthermore (wind tunnel and field) measurements are used to validate and improve the models. The capabilities of the resulting tools are demonstrated on a large scale rotor with and without flow control devices.The project is carried out by an absolute world class consortium since it consists of a selected group of participants from the subprogram aerodynamics of EERA Joint Program Wind (European Energy Research Alliance) in which all leading institutes on the field of aerodynamics participate, complimented with two leading industrial partners.