Although research on the role of verbal working memory (WM) in language processing has focused on phonological maintenance, considerable evidence indicates that maintenance of semantic information plays a more critical role. This paper reviews studies of brain damaged and healthy individuals, demonstrating the contribution of semantic WM to language processing. On the sentence comprehension side, semantic WM supports the retention of individual word meanings prior to their integration. It also serves to maintain semantic information in an activated state such that semantic interference between constituents in a sentence can be resolved. Phonological WM does not appear to contribute to either of these functions, though it contributes to verbatim sentence recall. On the production side, evidence points to the phrase as the minimal scope of advance planning in sentence formulation, with semantic WM supporting the representation of the meanings of content words within a phrase. Planning at the phonological level appears to have a very limited scope, making few demands on phonological WM. These findings imply that treatment of semantic but not phonological WM deficits should lead to improved sentence comprehension and production and preliminary findings (Harris, Olson, & Humphreys, 2014) support that view.