The Administration on Children, Youth, and Families and the Office of the Assistant Secretary for Planning and Evaluation have undertaken the National Survey of Child and Adolescent Well-Being (NSCAW). NSCAW makes available, for the first time, nationally representative longitudinal data drawn from first-hand reports of children and families or other caregivers who have had contact with the child welfare system. Data from service providers are also collected. NSCAW is the first national study to provide detailed information on the experiences of children and families with the child welfare system and to collect measures of well-being for this population. The NSCAW is designed to address the following questions: What paths do children follow into and through the child welfare system? What factors affect investigation, services, placements, and length of involvement? What are the long- and short-term outcomes for children and families in the child welfare system in terms of safety, well-being, and permanence? The target population for the NSCAW includes all children and families that enter the child welfare system. Two samples were drawn from the population in 92 participating county child welfare agencies throughout the nation. The CPS sample includes 5,501 children, who were between the ages of 0 and 14 years at the close of the investigation. All investigations for the sample were closed between October 1, 1999 and December 31, 2000. The second sample consists of an additional 727 children, who were in out-of-home care for about 12 months at the time of sampling. This second group, referred to as the One Year in Foster Care (OYFC) Sample, was selected to allow special analysis related to the experience of out-of-home care. Waves 2, 3, and 4 take place 12, 18, and 36 months after the close of the investigation. The NSCAW II study design essentially mirrors that of NSCAW I. The NSCAW II cohort includes 5,872 children, aged birth to 17.5 years old, who had contact with the child welfare system within a 15-month period that began in February 2008. Children were sampled from investigations closed during the reference period. The cohort of 5,872 children was selected from 81 of the original NSCAW 92 Primary Sampling Units (PSUs) in 83 counties in 30 states that agreed to participate in NSCAW II. Retaining most of the NSCAW I PSUs will allow researchers to assess the change in context from the late 1990s, and enable longitudinal analysis of organizational measures such as staff turnover, climate, and work environment. Like NSCAW I, NSCAW II is a longitudinal study with multiple informants associated with each sampled child, to get the fullest possible depiction of that child. Face-to-face interviews or assessments were conducted with children, parents, and nonparent adult caregivers (e.g., foster parents, kin caregivers, group home caregivers), and investigative caseworkers. Baseline data collection began in March 2008 and was completed in September 2009. The second wave of the study, 18 months after the close of the NSCAW II index investigation, began in October 2009 and was completed in January 2011. At Wave 3, children and families were reinterviewed approximately 36 months after the close of the NSCAW II index investigation. The NSCAW II cohort of children who were approximately 2 months to 17.5 years old at baseline ranged in age from 34 months to 20 years old at Wave 3. Data collection for the third wave of the study began in June 2011 and was completed in December 2012.