Abstract It is hypothesized that creole languages are largely invented by children and show fundamental similarities, which derive from a biological program for language. The structures of Hawaiian Pidgin and Hawaiian Creole are contrasted, and evidence is provided to show that the latter derived from the former in a single generation. A realistic model of the processes of Creole formation shows how several specific historical and demographic factors interacted to restrict, in varying degrees, the access of pidgin speakers to the dominant language, and hence the nature of input to the children of those speakers. It is shown that the resulting similarities of Creole languages derive from a single grammar with a restricted list of categories and operations. However, grammars of individual Creoles will differ from this grammar to a varying extent: The degree of difference will correlate very closely with the quantity of dominant-language input, which in turn is controlled by extralinguistic factors. Alternative explanations of the above phenomena are surveyed, in particular, substratum theory and monogenesis: Both are found inadequate to account for the facts. Primary acquisition is examined in light of the general hypothesis, and it is suggested that the bioprogram provides a skeletal model of language which the child can then readily convert into the target language. Cases of systematic error and precocious learning provide indirect support for the hypothesis. Some conjectures are made concerning the evolutionary origins of the bioprogram and what study of Creoles and related topics might reveal about language origins.