Non-polar surfaces of compound semiconductor materials are typically characterized by their low surface energies and charge neutrality. But the energetic positions of surface states are crucially determining the properties of a surface, especially during growth and within device applications. In order to reduce discontinuities of the polarization fields in GaN-based heterostructure device applications the switching to non-polar growth surfaces might be a reasonable solution. Furthermore, facets of nanostructured objects, such as e.g., semiconductor nanowires, are most likely formed by non-polar surfaces due to their low surface energy. In the Review@RRL by Holger Eisele and Philipp Ebert (pp. 359–369) the basic properties of group-III nitride semiconductor surfaces are reviewed up to their present knowledge. Based on the structural properties of these surfaces the electronic structure is discussed in comparison between theoretical calculations and experimental results. Particular attention is paid to the question of the energetic position of surface states and the Fermi level position with respect to the fundamental bulk band gap. When investigating these surfaces experimentally, the surface pinning is found to be a crucial effect, on which special attention has to be laid. Beside the intrinsic properties also extrinsic influences on these surfaces are reported, such as defects, adsorbents, and decomposition effects. Last but not least, doping-related effects at these surfaces are discussed.