The present work describes a method for the structural optimization of wind turbine rotor blades for given prescribed aerodynamic shape. The proposed approach operates at various description levels producing cost-minimizing solutions that satisfy desired design constraints at the finest modeling level. At first, a “coarse”-level constrained design optimization is performed by using a 1D spatial geometrically exact beam model for aero-servo-elastic multibody analysis and load calculation, integrated with a 2D FEM cross sectional model for stress/strain analysis and the evaluation of the 1D model fully-populated cross sectional stiffness matrices. Next, a “fine”-level 3D FEM model is used for the refinement of the coarse-level solution. Improved results obtained at the level of the 3D model are utilized at the following coarse-level iteration through a heuristic modification of the design constraints. In addition, a buckling analysis is performed at the fine description level, which in turn affects the non-structural blade mass. The updated constraint bounds and mass make their effects felt at the next coarse-level constrained design optimization, thereby closing the loop between the coarse and fine description levels. The multi-level optimization procedure is implemented in a computer program and it is demonstrated on the design of a multi-MW horizontal axis wind turbine rotor blade.