Children with Down syndrome are usually good communicators. They are keen to interact socially right from infancy but they have to rely on non-verbal skills such as gesture for longer than other children because they usually experience significant speech and language delay. Once they start to talk, they make good use of the speech and language skills that they have for the same range of communicative activities as everyone else, particularly if encouraged to do so by sensitive support from those around them at home, at school and in the community. However, they have specific difficulty with learning grammar and with developing clear speech. Some of the reasons for their difficulties with learning to talk are known and provide pointers to effective intervention strategies. Researchers and practitioners worldwide now agree on the principles for effective intervention. Since speech and language skills are central to the development of mental abilities such as thinking, reasoning and remembering as well as to social inclusion, it is essential that speech and language is a focus for parents, teachers and therapists from infancy through to adult life. This overview covers development from birth to teenage years, and to understand the speech and language needs of primary and secondary age children, teachers and parents are encouraged to read the whole overview as the children’s difficulties have their roots in the preschool years.