This book and its companion volume present a detailed guide to three major structural-functional theories: Functional Grammar, Role and Reference Grammar and Systemic Functional Grammar. This first volume provides the necessary background through a discussion of the characteristics of functional theories, followed by a brief analysis of six approaches to language in the light of this discussion. These chapters lead to a characterization of a smaller set of 'structural-functional grammars', among which FG, RRG and SFG are central. An overview of each of these theories in relation to the simplex clause is then presented, followed by a more critical comparison. The remainder of the book deals with the structure and meaning of phrasal units, the representation of situations, and the treatment of tense, aspect, modality and polarity, across the three theories. A major feature of the book is the use of examples from corpora of English and other languages, which serve not only to exemplify theoretical and descriptive claims, but also at times to challenge them.