Conventional photolithographic rapid prototyping approaches typically achieve reaction confinement in depth through patterned irradiation of a photopolymerizable resin at a wavelength where the resin strongly absorbs, such that only a very thin layer of material is solidified. Consequently, three-dimensional objects are fabricated by progressive, two-dimensional addition of material, curtailing fabrication rates and necessitating the incorporation of support structures to ensure the integrity of overhanging features. Here, we examine butyl nitrite as a UV-active photoinhibitor of blue light-induced photopolymerizations and explore its utilization to confine in depth the region polymerized in a volume of resin. By employing two perpendicular irradiation patterns at blue and near-UV wavelengths to independently effect either polymerization initiation or inhibition, respectively, we enable three-dimensional photopolymerization patterning in bulk resin, thereby complementing emergent approaches to volumetric 3D printing.