Variable stiffness laminates are advanced composite concepts. For these laminates the material stiffness is considered as a spatially distributed property which can be tailored to specific loading conditions. One of the most recent concepts used for variation of material properties is fiber steering in composite skins. The increase in design freedom going from constant to variable stiffness laminates, requires dedicated design tools, where the optimization-based methods being the most appropriate. Besides, in airframe structures, the thin wall skins are usually reinforced using various types of stiffeners. Therefore, a design methodology/tool is required to find the optimum fiber steered stiffened structure. In a close collaboration with the University of South Carolina, USA, we are developing new methods and tools for design optimization of advanced tow steered composites for aircraft structures.