Language is a highly complex, specialised cognitive ability that is unique to humans. Nevertheless, most three-year-olds can talk using simple sentences. However, seven per cent of otherwise normally developing children have ‘specific language impairment’ (SLI), and many of these children have dyslexia too. SLI has a strong genetic component and for many individuals it is a life-long impairment. The long-term costs are socially, culturally, and economically high. I will present some research findings, using traditional and brain imaging techniques to explain these children’s language problems. SLI provides a unique window into the brain, how specialised systems develop, and how our findings can help children.