AbstractAlthough there is considerable variability, most individuals with Down syndrome have mental retardation and speech and language deficits, particularly in language production and syntax and poor speech intelligibility. This article describes research findings in the language and communication development of individuals with Down syndrome, first briefly describing the physical and cognitive phenotype of Down syndrome, and two communication related domains—hearing and oral motor skills. Next, we describe language development in Down syndrome, focusing on communication behaviors in the prelinguistic period, then the development of language in children and adolescents, and finally language development in adults and the aging period. We describe language development in individuals with Down syndrome across four domains: phonology, semantics, syntax, and pragmatics. Wethen suggest strategies for intervention and directions for research relating to individuals with Down syndrome. © 2007 Wiley‐Liss, Inc. MRDD Research Reviews 2007;13:2