Abstract: An airfoil particularly suited for use in rotor blades of large wind-driven ower plants is formed in three modular sections including a nose or leading section, a spar section and a trailing section, each separately formed and subsequently assembled. In the method of the invention the spar section is formed in two separate mold units which are configured to form part of the upper and lower aerodynamic profile of the airfoil and the two spar section units are trimmed along a junction plane and then joined together at the junction plane to form the spar section of the airfoil.