Offering an introduction to the major concepts which characterize Systemic Functional Linguistics (SFL), this chapter is designed to provide an overview of the ‘contents’ of the theory. A Systemic Functional approach looks at how language functions to make meaning in context of situation. The chapter sets out the key concepts related to meaning within SFL theory, including what is meant by the notion of ‘acts of meaning’, before moving on to describe the place of grammar within the framework. How the grammar enables the meaning-making potential in language is explained in terms of the relationship it has within SFL’s general theory of meaning. Thereafter the three main components of meaning are explained in turn, representing ideational, interpersonal and textual meaning. After explaining the Marxist orientation of the theory, the chapter explains how SFL offers insight into how language is learnt and how language eventually evolves into the adult language system with the three major components of meaning. As a theoretical overview, this chapter provides a basis for the detailed consideration given to each of these areas in the remaining chapters of the volume.