By using metalorganic chemical vapor deposition, ZnO nanorods, nanotubes, and nanowalls can be selectively obtained by adjusting the growth pressure from 10 to 0.06 Torr. The appearance of different nanostructures is due to different growth modes. The variation of nanostructure shape with change in pressure is explained in terms of surface-to-volume ratio. Photoluminescence measurements show that growth at low-pressure facilitates the incorporation of acceptors in ZnO.