Copper (Cu) is a vital mineral essential for many biological processes. The vast majority of all Cu in healthy humans is associated with enzyme prosthetic groups or bound to proteins. Cu homeostasis is tightly regulated through a complex system of Cu transporters and chaperone proteins. Excess or toxicity of Cu, which is associated with the pathogenesis of hepatic disorder, neurodegenerative changes and other disease conditions, can occur when Cu homeostasis is disrupted. The capacity to initiate oxidative damage is most commonly attributed to Cu-induced cellular toxicity. Recently, altered cellular events, including lipid metabolism, gene expression, alpha-synuclein aggregation, activation of acidic sphingomyelinase and release of ceramide, and temporal and spatial distribution of Cu in hepatocytes, as well as Cu-protein interaction in the nerve system, have been suggested to play a role in Cu toxicity. However, whether these changes are independent of, or secondary to, an altered cellular redox state of Cu remain to be elucidated.