This paper represents a preliminary attempt to determine universals of grammatical development in children. On the basis of language acquisition data, a limited number of findings are presented in the form of suggested developmental universals. These universals are grouped according to the psychological variables which may determine them, in the hope that it may someday be possible to predict facts of linguistic development from principles of mental development. The underlying assumption of this work is that the child brings certain operating principles to bear on the task of learning to speak. Some of these principles stem from his general cognitive development and some are a product of his psychological capacity to process and store information. Some of the latter principles may be specific to the manipulation of language but no particular claim is made here as to their innateness. Two broad aspects of mental development are considered. The first section of the paper deals with developing cognition of the social and material worlds (cognitive variables); the second section deals with the particular abilities of the human mind to deal with linguistic structures (language processing variables). The discussion is limited to the development of grammar. (Author/FWB)