Written for the general reader, this text addresses one of the most fundamental biological questions: how a single cell, the fertilized egg, gives rise to the complete forms that make up the human adult. The answer lies in cell behaviour and how this behaviour is controlled by genes. Most of the book is devoted to embryonic development, but there are also chapters on the mechanisms used by animals that can regenerate their limbs or tails, on the processes of growth and ageing, and on cancer which is viewed as an abnormal developmental process. Finally, the relationship between development and evolution is explored. Recent years have seen considerable advances in our understanding of the principles which underlie the answers to these questions, but the story is by no means complete. Professor Wolpert believes that at some deep level there are only a few basic mechanisms that are used in the development of all animals and that these unifying principles can explain most of what we see.