Horizontal alignment of single-walled carbon nanotubes (SWNTs) in large-area (square centimeter scale) films is achieved by a facile approach. Combining in situ arc discharge growth of SWNTs with a weak (0.56 T) magnetic field allows aligned SWNT films to be fabricated on various substrates, including flexible plastics. Moreover, the film size, thickness, location and orientation can all be controlled.