This document is a description of the National Children's Study, the largest long-term study of children's health and development ever to be conducted in the United States. The National Children's Study reaffirms the federal government's commitment to the health and well being of children by drawing together the nation's top experts on child health and the environment in an unprecedented collaboration. Multiple federal agencies, national non-profit groups, community health care providers, and more than 100,000 families stand poised to help child health move forward in the 21st century. The goals of the Study complement government efforts to challenge individuals, communities, and professionals to take action to ensure that good health and long life are enjoyed by all. The Study also supports national goals to enhance education, for instance, by exploring the role of children's environments on their readiness to learn. This document is organized in the following sections: (1) Building the National Children's Study; (2) Moving Forward: Meeting the Challenges of the National Children's Study; and (3) Expressing the Vision for the National Children's Study.