The robust design of horizontal axis wind turbines, including both parameter and tolerance designs, is presented. A simple way of designing robust horizontal axis wind turbine systems under realistic conditions is outlined with multiple design variables, multiple objectives, and multiple constraints simultaneously by using the traditional Taguchi method and its extensions. The performance of the turbine is predicted using the axial momentum theory and the blade element momentum theory. In the parameter design stage, the energy output of the turbine is maximized using the Taguchi method and an extended penalty-based Taguchi method is proposed to solve constrained parameter design problems. Using an appropriate set of tolerance settings of the parameters, the tolerance design problem is formulated so as to yield an economical design while ensuring a minimal variability in the performance of the wind turbine. The present work provides a simple and economical approach for the robust optimal design of horizontal axis wind turbines.