In Chapter 3 we examined the ubiquity of chunks in everyday spoken language, focusing on the high-frequency chunks which oil the interpersonal wheels of conversation. We argued that such chunks have often not been given the status they deserve as an important part of the vocabulary. However, some chunks are quite low in frequency and quite opaque in terms of their meaning, and yet have long been favoured by pedagogy; these are usually called idioms. Everyone loves idioms, teachers and learners alike. They offer a colourful relief to what can otherwise be a rather dull landscape of grappling with difficult grammar rules, learning new word lists, doing tests, and so on. Publishers are aware of this and offer materials specially devoted to idiom-learning, and there are good learners' dictionaries of idioms available for English, including corpus-based ones. A search through the back issues over decades of important language teaching journals such as ELT Journal and TESOL Quarterly will reveal continual mention of idioms, usually as part of vocabulary teaching or the teaching of language and culture, and mostly not seen as anything special or peculiar in the language teaching repertoire, albeit a challenge. However, in a book by one of the authors of this book (McCarthy 1998), it was noted that there was a shortage of information on how idioms are actually used in everyday communication, and it was argued that better information on actual use might benefit pedagogy.