The National Institute of Child Health and Human Development (NICHD) Study of Early Child Care is an ongoing, prospective, 3-year longitudinal study of over 1,300 full-term healthy infants and families from 10 sites across the United States. While the sample is not nationally representative, the subjects come from major regions of the country: the East Coast, the West Coast, the Mid-West, the North, and the South. They come from urban and from rural settings, and include minorities as well as single-parent and two-parent families. The study examines the concurrent, long-term, and cumulative influences of variations in early child care experiences on the cognitive, linguistic, social, emotional, and physical development of infants and toddlers. The study design takes into account the complex interactions among characteristics of the family and home, of the child care environments, and of the child. Subject recruitment started in January 1991, and data collection was scheduled to end at the beginning of 1995. Data collection involved periodic telephone calls to families beginning at 3 months and home visits, child care center visits, or laboratory assessments at 1, 6, 15, 24, and 36 months. This document is volume 3 of a 5-volume operations manual that explains, in 29 chapters, the procedures used in conducting the NICHD study. Volume 3 consists of chapters 13 through 19. Chapter 13 provides instructions for conducting follow-up telephone interviews at 13 and 23 months. Subsequent chapters mostly address the 15-month visits and assessments. Chapter 14 presents an overview of the visits to the child's home and child care center, and laboratory assessments at 15 months. Chapter 15 provides information on conducting home visits, instructions for conducting a home environment inventory, procedures for videotaping mother-child interactions, information on standardized interviews and questionnaires, and procedures to use when the subject mother and child are not living in the same household. Instructions for conducting visits with fathers are given in chapter 16. Chapter 17 provides instructions for: (1) conducting the 15-month laboratory visit; (2) observing and coding children's solitary play; (3) conducting the Strange Situation Procedure; (4) administering the Bayley Scales of Infant Development; and (5) measuring children's physical growth. The procedure for visiting subject children's child care centers is explained in chapter 18. Chapter 19 presents instructions on making follow-up telephone calls at 18 and 21 months. (BC)