This paper describes in detail the elements of social behaviour and social organizations of four closely related rodents (Notomys alexis, Pseudomys albocinereus, P. shortridgei and P. desertor) from diverse habitats, and the social organizations of seven other conilurine rodents are described briefly. Most of the data were determined from quantitative observations of animals caged in twos or in larger groups for at least ten days. Breeding pairs were observed daily throughout pregnancy and parenthood. A dispersed organization and three types of communal organization are described, and evolutionary trends in dispersion and territoriality, cohesion, communication and co-operation are discussed.