Wilson disease is an autosomal recessive inherited disorder of copper metabolism, characterized by the accumulation of copper in the body due to defective biliary copper excretion from hepatocytes. Recently, novel components involved in copper metabolism, including Menkes disease protein (ATP7A), Wilson disease protein (ATP7B), and copper chaperones, have been identified. It has been demonstrated that ATP7B functions in copper secretion into the plasma, coupled with ceruloplasmin synthesis and biliary copper excretion. However, the precise intracellular localization of ATP7B has been disputed. Various mutations of ATP7B have been reported in patients with Wilson disease, and investigations of genotype-phenotype correlations are now being conducted in the patients. These recent findings provide us with information on the molecular pathogenesis of Wilson disease, as well as the biological mechanisms of copper homeostasis. In this review, recent advances in this field are briefly summarized.