Testimony, the transmission of knowledge through communication, requires a shared understanding of linguistic expressions and utterances of them. Is this understanding itself a kind of knowledge, knowledge of meaning? The intuitive answer is ‘yes’, but the nature of such knowledge is controversial, as is the assumption that understanding is a kind of knowledge at all. This article is a critical examination of recent work on the nature and role of semantic knowledge in the generation of the linguistic understanding needed for testimony. After describing a default view – that linguistic understanding partially consists in the possession and application of knowledge of a compositional theory of truth conditions – it scrutinizes two recent charges against this view: that linguistic understanding and knowledge of meaning are conceptually distinct, and that semantic ‘knowledge’ is knowledge without an object.