Abstract: The cellular uptake and intracellular distribution of the essential but highly toxic nutrient, copper, is a precisely orchestrated process. Copper homeostasis is coordinated by several proteins to ensure that it is delivered to specific subcellular compartments and copper-requiring proteins without releasing free copper ions that will cause damage to cellular components. Genetic studies in prokaryotic organisms and yeast have identified membrane-associated proteins that mediate the uptake or export of copper from cells. Within cells, small cytosolic proteins, called copper chaperones, have been identified that bind copper ions and deliver them to specific compartments and copper-requiring proteins. The identification of mammalian homologues of these proteins reveal a remarkable structural and functional conservation of copper metabolism between bacteria, yeast and humans. Furthermore, studies on the function and localization of the products of the Menkes and Wilson's disease genes, which are defective in patients afflicted with these diseases, have provided valuable insight into the mechanisms of copper balance and their role in maintaining appropriate copper distribution in mammals.