The chapter deals with functional approaches to mood and modality. The focus is on Systemic Functional Grammar (SFG) associated with Halliday’s writings, Dik’s Functional Grammar (FG), and the mainly American functional school of Role and Reference Grammar (RRG). The positions taken by these schools can be described as “structuralist-functionalist” in that they propose models relating form to function. It is shown that a layered representation in some form is required to account for the role of mood and modality. Halliday’s interpersonal grammar has been further developed under the heading of Appraisal. It is typical of this and related theories that it emphasizes the similarity between modality and other types of attitudes which can be expressed by language.