UV−visible diffuse reflectance spectroscopy was used to probe the electronic structure and domain size of tungsten oxide species in crystalline isopolytungstates, monoclinic WO3, and dispersed WOx species on ZrO2 surfaces. UV−visible absorption edge analysis, CO2 chemisorption, and Raman spectroscopic results show that three distinct regions of WOx coverage on ZrO2 supports appear with increasing WOx surface density: submonolayer region (0−4 W nm-2), polytungstate growth region (4−8 W nm-2), and polytungstate/crystalline WO3 coexistence region (>8 W nm-2). The structure and catalytic activity of WOx species on ZrO2 is controlled only by WOx surface density (W nm-2), irrespective of the WOx concentration, oxidation temperature, and ZrO2 surface area used to obtain a particular density. The submonolayer region is characterized by distorted octahedral WOx species that are well dispersed on the ZrO2 surface. These species show a constant absorption edge energy, they are difficult to reduce, and contain few a...