Nanocrystalline Zn1-xCoxO (x = 0.020, 0.056, and 0.098) powders exhibit intrinsic high-temperature ferromagnetism, as suggested by the well-defined hysteresis loops shown in the figure. The origin of this ferromagnetism is thought to be electron transfer from host Zn 4s states to unfilled dopant Co 3d states (shown in the inset to the figure), which leads to the formation of a spin-split impurity band at the Fermi level in the gap.