What is art? Must it be a unique, saleable luxury item? Can it be a concept that never takes material form? Or an idea for a work that can be repeated endlessly? Conceptual art favours a vivid engagement with such questions. It can take many forms: photographs, videos, posters, billboards, charts, plans and, in particular, language itself. Tony Godfrey has written the first ever clear, extensive, concise and informative account of this fascinating phenomenon.