The blue coloured plasma protein ceruloplasmin binds up to 95% of circulating copper, and has several possible functions. It has been proposed to function in copper transport, oxidation of organic amines, iron(II) oxidation and the regulation of cellular iron levels, and catechols, radical scavenging and other antioxidant processes. This account will consider the relative importance of these multiple functions in terms of the physiological roles of ceruloplasmin.