Slang is used widely and often, typically associated with the writers of noir fiction, teenagers, and rappers, but also found in the works of Shakespeare and Dickens. It has been recorded since at least 1500 AD, and today's vocabulary, taken from every major English-speaking country, runs to over 125,000 slang words and phrases. Jonathon Green's wide-ranging tour of this fascinating sub-set of the English language considers the meaning and origins of the word 'slang' itself, the ideas that a make a word 'slang', the long-running themes that run through slang, and the history of its many dictionaries.