Specific language impairment (SLI) in children has been discussed as a clinical diagnostic categorysince Benton first suggested its existence in 1964. A common criticism of the construct of SLI has been the basis of the diagnosis on exclusionary criteria rather than inclusionary linguistic descriptions. Historically, children with SLI have been diagnosed based on the clinical categories they do not fit into, for example intellectual disability or hearing impairment. The clinical group of children with SLI is therefore a heterogeneous group of language-impaired individuals who have little in common except what they are not. Recently, however, researchers have begun suggesting explanatory hypotheses about the nature of the impairment, delineating the language characteristics of children with SLI and attempting to link the characteristics to models of linguistic organisation. The purpose of this article is to review the SLlliterature. In particular, the impact current research has had on the understanding of SLI and the directions current research is taking are discussed.