In recent linguistic theory, there has been an explosion of detailed studies of language variation. This volume applies such recent analyses to the study of child language, developing new approaches to change and variation in child grammars and revealing both early knowledge in several areas of grammar and a period of extended development in others. Topics dealt with include question formation, subjectless sentences, object gaps, rules for missing subject interpretation, passive sentences, rules for pronoun interpretation and argument structure. Leading developmental linguists and psycholinguists show how linguistic theory can help define and inform a theory of the dynamics of language development and its biological basis, meeting the growing need for such studies in programs in linguistics, psychology, and cognitive science.