Human language is a weird communication system: it has more in common with birdsong than with the calls of other primates. In this clear and non-technical overview, Jean Aitchison explores why it evolved and how it developed. She likens the search to a vast prehistoric jigsaw puzzle, in which numerous fragments of evidence must be assembled, some external to language, such as evolution theory and animal communication; others internal, including child language, pidgins and creoles, and language change. She explains why language is so strange, outlines recent theories about its origin, and discusses possible paths of evolution. Finally, she considers what holds all languages together, and prevents them from becoming unlearnably different from one another.