The Early Childhood Longitudinal Study, Birth Cohort 2000 (ECLS-B) is a study that will assess children's health status and their growth and development in domains that are critical for later school readiness and academic achievement. This paper is one of several that have been prepared in support of ECLS-B design efforts. It is anticipated that three waves of data will be collected from families of children born between January and December 2000, with supplementary data collected from child care providers. Several options remaining to be decided are addressed, including identifying the primary respondent and other respondents, the assessments to be used, and how to collect data on variables such as other children in the family. The following eight major domains have been identified for the study: (1) demographic background; (2) family organization, composition, history, and turbulence; (3) family processes; (4) child care; (5) child characteristics; (6) child outcomes; (7) early health care, feeding patterns, nutrition, and insurance; and (8) distal constructs, such as neighborhood characteristics. Each of these domains is discussed. (Contains 485 references.) (SLD)