Interest in how children acquire language has a long history, with links to, amongst other disciplines, biology, neuroscience, anthropology and philosophy, as well as the perhaps more obvious linguistics, psychology and sociology. The different research traditions of these disciplines tend to emphasise different aspects of the learning process, rely on different kinds of evidence for their validity, and lead to different theoretical interpretations of what may be happening as children try to make sense of their spoken environment. (For overviews of the field at different points in time, see Gleason and Weintraub 1978: 171-83; Ochs 1979; Nicholls and Wells 1985: 2-7; Mitchell and Myles 1998; Sealey 2000; Oates and Grayson 2004.) I have chosen to cluster the various traditions into three broad perspectives and, for the sake of clarity, I emphasise the differences rather than the commonalities between them, although in practice there is considerable overlap and the proponents of each have built on each other’s insights, as well as occasionally challenging what has gone before.