The click reaction paradigm is focused on the development and implementation of reactions that are simple to perform while being robust and providing exquisite control of the reaction and its products. Arguably the most prolific and powerful of these reactions, the copper-catalysed alkyne-azide reaction (CuAAC) is highly efficient and ubiquitous in an ever increasing number of synthetic methodologies and applications, including bioconjugation, labelling, surface functionalization, dendrimer synthesis, polymer synthesis and polymer modification. Unfortunately, as the Cu(I) catalyst is typically generated by the chemical reduction of Cu(II) to Cu(I), or added as a Cu(I) salt, temporal and spatial control of the CuAAC reaction is not readily achieved. Here, we demonstrate catalysis of the CuAAC reaction via the photochemical reduction of Cu(II) to Cu(I), affording comprehensive spatial and temporal control of the CuAAC reaction using standard photolithographic techniques. Results reveal the diverse capability of this technique in small molecule synthesis, patterned material fabrication and patterned chemical modification.