The National Children's Study is the largest long term study of children's health and development ever to be conducted in the United States, involving 100,000 children from before birth to age 21. The Study aims to better understand the link between the environments in which children are raised and their physical and mental health and development. By looking for relationships between environments and children's physical and mental progress, the Study seeks to find basic causes of many of today's major childhood diseases and disorders and to determine not only which aspects of the environment are harmful, but also which factors are harmless or helpful to children's health and development. The Study will focus on a set of key scientific research questions that address some of the most pressing health and development concerns for children today, including: (1) Pregnancy-related outcomes; (2) Injury; (3) Asthma; (4) Obesity, diabetes, and physical development; and (4) Outcomes related to child development and mental health. The Study will provide information to help generations of Americans meet the health, economic, and social challenges associated with many serious health conditions. It will build a source of data that may answer questions about links between environments and the origins of childhood and adult diseases.