The use of two orthogonal, external fields is shown to control the orientation of lamellar microdomains in three dimensions in diblock copolymer thin films. An elongational flow field was applied to obtain an in-plane orientation of the microdomains of the copolymer melt, and an electric field, applied normal to the surface, was then used to further align the microdomains. Thin films of symmetric diblock copolymers of poly(styrene-b-methyl methacrylate) with long-range order and orientation of the lamellar microdomains were obtained as evidenced by small-angle X-ray scattering and transmission electron microscopy.