Firth’s (1968 [1957]) speech-theoretical perspective is at the root of the term ‘register’ in modern linguistics. In contrast to the formalistic line of American structuralism, Firth postulated that linguistic signs relate directly to the context, i.e. their usage depends on the context-of-situation. Firth’s examples are often from the realm of ‘restricted languages’: the language for regulating air traffic, weather forecasts, congratulation cards, and in simplified registers of game instructions (chess, bridge). In these examples, the stable connection between context and linguistic-communicative patterns is evident. Firth’s aim is an integrated theory of meaning in which the speech users and their speech usage are given equal status. The term ‘register’ was introduced by the Firthian linguist Reid (1956). The first conceptual and theoretical elaboration of the term can be found in Halliday, McIntosh & Strevens (1964), a book on applied linguistics. The basic idea underlying this essay, which is to base the notion dialect on the dimension speech user and the notion register on the dimension speech usage, is described fully in Halliday’s Language as social semiotic (1978). The term ‘register’ is one of the fundamental pillars of the Hallidayan conception of sociolinguistics.