An airfoil box and associated method are provided. The airfoil box includes two or more half-shell structures. Each half-shell structure is an integral or unitary member that includes at least a portion of the outer skin of the airfoil as well as stiffener members and connection members. For example, the half-shell structures can be integrally formed of composite materials. The half-shell structures can be assembled by connecting the connection members with fasteners such as rivets to form the airfoil box.