Morphology-controlled nano- and microcrystals of ZnO (see figure) with different ratios of polar to nonpolar faces were synthesized through a soft-solution process. With these crystals, it is clearly demonstrated that a ZnCl nanoplate with a large population of polar Zn(0001) faces is the most photocatalytically active morphology, underscoring the importance of the fine-tuning of face orientation in optimizing the activity of photocatalysts.