Electronic language corpora, and their attendant computer software, are proving increasingly influential in language teaching as sources of language descriptions and pedagogical materials. However, few teachers are clear about their nature or their relevance to language teaching. This paper defines corpora and their types, discusses their contribution to language learning and teaching, and provides examples of their use in class. It also outlines the changes in knowledge, skills and attitudes that are needed for learners and teachers to take advantage of the opportunities offered by the availability of corpus resources. Finally, the paper discusses the limitations of using corpora in language teaching, and the potential pitfalls arising from their uncritical use. Although the paper refers to research and teaching materials and procedures relevant to English language teaching (ELT) it addresses issues related to language teaching in general.