ZnO has hexagonal wurtzite structure that is characterized by a mixture of ionic and covalent bondings between Zn and O atoms. A Zn atom is surrounded by four O atoms, or vice versa, which are located at the edges of a tetrahedron. Such coordination gives rise to polar symmetry along the c-axis of the hexagonal structure. The polarity affects electrical, optical, mechanical, and chemical properties of ZnO. In 2000, we have reported the successful selective growth of polarity-controlled ZnO films by molecular-beam epitaxy (MBE) using either GaN templates or MgO buffer. We confirmed different growth behaviors on the surfaces of ZnO layers with different polarities. Recently, we have explored the effect of crystal polarity on the formation of ZnO nanostructures. The periodically polarity-inverted (PPI) ZnO templates with submicron line-pitch over a large area were fabricated using MBE by employing MgO buffer layers and lithography technique. We grew ZnO nanorods using chemical transport and condensation method. The ZnO nanorods grew only on Zn-polar regions with the same periodicity as that of PPI template, which eventually produces well-aligned ZnO nanorod arrays.