Establishing which neural systems support processing of signed languages informs a number of important neuroscience and linguistic questions. First, what constitutes the 'core language system' - what areas of the brain are involved in language processing regardless of the modality? Evidence will be presented from studies of signers with acquired language impairments as a result of stroke and from functional imaging studies of the processing of BSL and English. Second, do sign language sentences encoding spatial concepts differ from more abstract sentences - does sign language recruit nonlinguistic conceptual structures? Results of a study on the processing of BSL sentences with topographic and non-topographic structure will be discussed in relation to this question. The conclusion returns to a consideration of the nature of the 'core language system' and spoken language.