The complement system is a key factor in host defence against infection and also plays important parts in many other biological systems, notably immune complex handling and the generation of an immune response. Complement has also been implicated as a pathogenic factor in many inflammatory and infectious diseases. Despite these numerous physiological and pathological roles, complement, the dreaded “C-word”, remains unloved by most students of immunology and medicine. Perhaps the major problem limiting the appeal of complement is the archaic and illogical terminology that characterises the field, remnants of the historical roots of discovery of complement. Those “in the know” realise that the terminology is a minor inconvenience; the problem lies in convincing …