Why does language change? Why can we speak to and understand our parents but have trouble reading Shakespeare? Why is Chaucer's English of the fourteenth century so different from Modern English of the late twentieth century that the two are essentially different languages? Why are Americans and English 'one people divided by a common language'? And how can the language of Chaucer and Modern English - or Modern British and American English - still be called the same language? The present book provides answers to questions like these in a straightforward way, aimed at the non-specialist, with ample illustrations from both familiar and more exotic languages.