Zinc oxide (ZnO) is an important material in heterogeneous catalysis and has recently attracted interest as a wide band-gap semiconductor for electro-optical devices. The surfaces and interfaces of ZnO are critical for understanding the mechanistics of surface chemical reactions and for the fabrication of high quality hetero- and homoepitaxial films with long-term stability. The surfaces of the main low-index planes, i.e., surfaces with (0 0 0 1), (0 0 0 1), (10 10), (1 1 2 0) and (1 1 2 1) orientations are characterized with high-resolution scanning tunneling microscopy and compared to first-principles total-energy calculations. (C) 2004 Published by Elsevier B.V.