This is the tenth edition of a classic work on child development by Ronald Illingworth (1909-1990), the renowned English paediatrician who was Professor of Child Health at the University of Sheffield. This book was first published in 1960 and Professor Illingworth revised it frequently. It was translated into several languages and is used throughout the world. Since the publication of the ninth edition of this book in 1987, a sea of changes has happened in the discipline of child development. To bridge this gap Dr. MKC Nair and Dr. Paul Russell have supported Professor Illingworth's extraordinary observations with contemporary evidence whenever available. In addition, they have included the current normative values in child development as well as cultural and societal influences on a developing child. The Development of the Infant and Young Child by Dr Ronald S Illingworth is considered as the bible in the Growth and Development area. Every word of this book is considered as the Gospel truth by the Indian Paediatricians. The last edition of this book came out in 1999. This thoroughly revised and updated edition tries to bridge the gap between the last edition and current concepts