This study of the parasitic weaverbirds is an entity in itself, complete as far as available permit. It is also a part of a general survey of the problem of avian brood parasitism, in the course of which, besides many families of parasitic birds wre issued by the author on cowbirds (1929), on African cuckoos (1946), and on honey-guides (1955). To complete the series the author hopes to eventually publish a comprehensive comparative and interpretive summation of the biological aspects of the subject.