<p>Recent trend towards lightweight wind turbine blades led to slender design. These structures are more likely to undergo large deformations, thus experiencing geometric nonlinearities. Due to the large deformations, conventional linear theories cannot accurately model the blades because of the significance of nonlinear effects in large-scale wind turbines. In this paper, the coupled vibrations of a wind turbine blade subjected to aerodynamic loading are studied. Primary and combination resonances of the coupled first edge, first two flaps, and first torsion modes are investigated. Nonlinear equations of motion having cubic nonlinear terms are solved using multiple-scales perturbation method. During primary and combination resonances, the impacts of aerodynamic forcing term, tensile rigidity, and blade design parameters on steady-state responses are studied using the structural specifications of National Renewable Energy Laboratory (NREL) 5-MW reference horizontal axis wind turbine (HAWT) blade through frequency response curves. It is revealed that, depending on the system parameters, multiple equilibria coexist which may be a limit cycle or an irregular motion. The phenomena of energy transferring via internally resonating modes is observed during the combination resonance. Steady-state motions of flapwise and torsion modes are shown to vary with the design parameters.</p>