This book for the general reader addresses a fundamental and important biological question: How is it that a single cell, the fertilized egg, gives rise to the complete forms that make up the adult? How does it make so many millions of cells, many of very different specialized functions, in just the right proportions? How do they come to be organized into complete structures such as limbs, faces, or brains? How is it that the patterns are so stable and repeatable generation after generation? Where in the egg is all this information encoded or embedded? 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. Recently there have been 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. Not all of his co-workers would agree with him, and it is too soon to know whether he is wholly correct. But the insight he offers into the early stages of life provoke debate.