This chapter considers the structure of the clause from the perspective of the metafunctional choices that give rise to it. Experiential metafunction choices (Transitivity) are shown to lead to the number and nature of the basic constituents of the clause. Interpersonal metafunction choices (Mood and Modality) have realizations threaded in among the basic constituents. Textual metafunction choices (Theme and Given/New) relate to what comes at the beginning of the clause and what comes at the end. Remembering that an important concern of SFL is that it should be appliable to text analysis, the chapter includes discussion of how ‘probes’ are used in SFL to identify instances of categories in texts. An application of SFL of particular interest to the chapter’s author is that of discovering how children learn to write in different registers. Most of the exemplification of the theoretical points is from the work of an eleven-year-old girl, who provided a variety of pieces of writing from her different school courses. There is no room in the chapter for full discussion of her registers, but by implication the chapter shows how the analysis is relevant to such a study.