The chapters in this volume were originally separate research reports from longitudinal study of a group of four children. As a collection, the reports present a developmental story of language acquisition in the third year of life - a time of great achievement as children acquire a basic knowledge of semantics, syntax, and discourse. The early chapters show the children learning to form simple sentences; later chapters show them beginning to acquire the structures of complex sentences. Several conceptual themes in current language acquisition research and theory were first articulated in the studies reproduced here: the centrality of verbs for learning syntax; the role of meaning in acquisition; the importance of context; the relationship of language learning to other aspects of cognitive development; and individual differences among children learning the same language. These themes are discussed in an introductory chapter that unifies the studies and places the reports in the context of current research and theory in child language.