How does behaviour develop in humans and animals? What are the causal mechanisms governing this behaviour? These important questions are addressed in this book, first published in 1994. All the significant conceptual and empirical advances in this study of behavioural development are discussed in this volume by a wide range of scientists from different disciplines. A special feature of the approach taken here is that learning, as studied by experimental psychologists, is considered to be one process contributing to the development of the individual from conception to death. The development of the brain is also discussed in relation to behavioural processes. The book is dedicated to Jaap Kruijit, whose pioneering approach to the study of causal mechanisms of behavioural development has inspired many workers in this field. It will be an invaluable resource for advanced undergraduates, graduate students, and researchers in animal behaviour, psychology, and neuroscience.