Chapter 6 explores theme and information systems and structures. It concentrates on the need to argue from discourse semantics as far as the interpretation of information flow is concerned. This chapter brings some phonological analysis into the picture, since information systems are realised through prosodic phonology (i.e. rhythm and intonation). This work draws on Halliday’s analysis of English intonation, as presented in Halliday (1967, 1970) and Halliday & Greaves (2008).