Efforts to model the reactions of copper enzymes with dioxygen with low molecular weight complexes have been quite successful during recent years. Guided by Nature, intriguing model systems for the active sites of such proteins have been developed. In the course of these investigations, it has been discovered that a whole variety of copper−dioxygen adducts form when simple copper(I) complexes are oxidized with dioxygen. The course of these reactions depends on the temperature, the ligands present, and the solvent. The effects of these parameters (especially the effect of ligand modification) on the reactivity of copper(I) complexes towards dioxygen are discussed in detail in this review.