Corpora have had, and are still having, a huge impact on materials design. The compilation of dictionaries was one of the first areas to be influenced by corpora, but since that time they have gone on to inform the writing of a great range of materials. For example, corpus insight into the frequency of words or phrases can help textbook writers decide when certain target language is introduced. Greater understanding of collocation can also help textbook writers decide which items to introduce together. Some materials also include example concordances for learners to look at, or useful information about the relative frequency of certain items in written or spoken language. This unit considers the impact of corpora on the preparation of both grammar and vocabulary materials at sentence level and beyond.