This literature review examines calculators in the primary school classroom in light of their recent prohibition for younger children in England. Contrary to political fears about calculators being harmful, the existing literature indicates that calculators have many benefits: they can develop conceptual understanding, support and improve mental and written methods, be a stimulus for dialogic talk, provide instant feedback and help to develop key mathematical ideas such as 'number sense'. The ingrained nature of teacher attitudes, in particular relation to what skills they believe an effective mathematician requires, is explored and a link made between such attitudes and the potential use of calculators. Greater clarity is needed regarding what fundamental mathematical understanding actually entails and a long-term strategy needs to be in place in order for pre-service teachers' underlying beliefs to change.