In this paper early and later development of knowledge of syntactic structures and this development in language-disordered children are reviewed. Theories that have been presented to account for syntactic development (cognitive, cognitive-semantic and social-environmental) are discussed. Early developmental data indicate that there is not a semantic and then, later, a syntactic stage. As children acquire the meaning of a linguistic relation they simultaneously form hypotheses about the syntactic rules used to express this meaning. Abilities which play the most important role in development of comprehension of syntactic structures are the following: to process increasing amounts of parallel temporal-acoustic linguistic information and situational information, to form hypotheses about structures represented in this information, and to hold information in short-term memory so that it can be decomposed by retrieval of structures from long-term memory. The production of utterances, in addition, requires the programming of this parallel information into articulatory movements. Thus, differing language disorders are a reflection of varying degrees of difficulty in these abilities. Social-environmental factors can enhance or retard development, and, to some extent, compensate for differences from the norm in these abilities. (Author)